I am trying to search a List for combinations that add up to a particular value (I've tried using Knapsack but it was checking too much for my particular scenario and taking too long). The code works and finds matches for most of the datasets I throw at it but fails for some others.
All of my List s don't have more that 100 entries.
I had assumed that because my recursive method is wrapped in a sensible if statement that a stack overflow would not occur but it blows up on this line: if(x.Sum(y => y.Amount) == limit)
Here is my code:
private static void Check(List<double> trackedListToCopy, double limit)
{
List<CheckerObject> trackedList = new List<CheckerObject>();
int idCount = 1;
trackedListToCopy.ForEach(x => {
trackedList.Add(new CheckerObject() { Amount = x, Id = idCount});
idCount++;
});
List<List<CheckerObject>> possiblitiesToCheck = new List<List<CheckerObject>>();
if (trackedList.FirstOrDefault(x=>x.Amount == limit) != null)
{
Console.WriteLine("Exact match found");
return;
}
trackedList.ForEach(item =>
{
var listToCheck = new List<CheckerObject>();
if (trackedList.First().Id == item.Id)
return;
listToCheck.Add(trackedList.First());
listToCheck.Add(item);
possiblitiesToCheck.Add(listToCheck);
if (possiblitiesToCheck.Any(x => x.Sum(y => y.Amount) == limit))
{
List<CheckerObject> match = possiblitiesToCheck.First(x => x.Sum(y => y.Amount) == limit);
Console.WriteLine("Match found with 2 entries" + match);
return;
}
});
var baseList = new List<List<CheckerObject>>(possiblitiesToCheck);
SubsequentCheck(baseList, trackedList, limit);
}
private static void SubsequentCheck(List<List<CheckerObject>> baseList, List<CheckerObject> trackedList, double limit)
{
//List<List<CheckerObject>> copy = new List<List<CheckerObject>>(baseList);
trackedList.ForEach(item => {
baseList.ForEach(x =>{
if (!x.Contains(item))
{
x.Add(item);
if(x.Sum(y => y.Amount) == limit)
{
string show = "";
x.ForEach(n => { show += n.Amount + ","; });
Console.WriteLine(String.Format("Match Found from {0}", show));
}
if (x.Sum(y => y.Amount) < limit)
{
SubsequentCheck(new List<List<CheckerObject>>(baseList), trackedList, limit);
}
}
});
});
}
public class CheckerObject
{
public int Id { get; set; }
public double Amount { get; set; }
}
Any and all help is as always greatly appreciated.
Change
private static void SubsequentCheck(List<List<CheckerObject>> baseList, List<CheckerObject> trackedList, double limit)
to
private static void SubsequentCheck(List<List<CheckerObject>> baseList, List<CheckerObject> trackedList, double limit, int recursiveDepth = 0)
and
if (x.Sum(y => y.Amount) < limit)
{
SubsequentCheck(new List<List<CheckerObject>>(baseList), trackedList, limit);
}
to
if (x.Sum(y => y.Amount) < limit)
{
SubsequentCheck(new List<List<CheckerObject>>(baseList), trackedList, limit, recursiveDepth + 1);
}
Then log everything or put a conditional breakpoint on recursive depth greater than some sensible limit.
Also change the .ForEach calls to foreach loops so that the loop can be stopped properly for efficiency (the return statement does not end the loop in this case)
Also change the Lists for Hashsets when calling .Contains so frequently if performance is an issue
Related
I would like to have a "percent change for 'Investigations' and 'Breaches' by each quarter. I'm currently grouping by quarter and getting counts but I cannot figure out how to add percent change.
This is what I want to have a IEnumerable/List of:
public class StatusCountDto
{
public string Quarter { get; set; }
public int Investigations { get; set; }
public double InvestigationsChange { get; set; }
public int Breaches { get; set; }
public double BreachesChange { get; set; }
}
Currently I am grouping by the Quarter and getting counts but I cannot figure out how to get the percent change of Investigation counts and Breaches counts from the previous quarter.
The data is already sorted by Quarter. If the previous value doesn't exit (first index) then it should be 0.
This is what I have so far.
Metrics.GroupBy(m => m.Quarter )
.Select((g, index) => new StatusCountDto
{
Quarter = g.Key,
Investigations = g.Count(),
Breaches = g.Where(a => a.Breach == "Yes").Count()
})
.ToList();
Is there a way to use the index to calculate the percent change?
Using an extension method based on the APL scan operator, which is like Aggregate but returns the intermediate results, you can run through the data and refer back to previous counts.
// TRes combineFn(TRes PrevResult, T CurItem)
// First PrevResult is TRes seedFn(T FirstItem)
// FirstItem = items.First()
// First CurItem = items.Skip(1).First()
// output is seedFn(items.First()), combineFn(PrevResult, CurItem), ...
public static IEnumerable<TRes> Scan<T, TRes>(this IEnumerable<T> items, Func<T, TRes> seedFn, Func<TRes, T, TRes> combineFn) {
using (var itemsEnum = items.GetEnumerator()) {
if (itemsEnum.MoveNext()) {
var prev = seedFn(itemsEnum.Current);
for (; ; ) {
yield return prev;
if (!itemsEnum.MoveNext())
yield break;
prev = combineFn(prev, itemsEnum.Current);
}
}
}
}
Given this variation of Scan that uses a lambda to seed the result stream, you can use it to compute the whole stream:
var ans = Metrics
.GroupBy(m => m.Quarter)
.Select(g => new {
Quarter = g.Key,
Investigations = g.Count(),
Breaches = g.Count(a => a.Breach == "Yes")
})
.Scan(f => new StatusCountDto { // first result
Quarter = f.Quarter,
Investigations = f.Investigations,
Breaches = f.Breaches
},
(prev, cur) => new StatusCountDto { // subsequent results
Quarter = cur.Quarter,
Investigations = cur.Investigations,
InvestigationsChange = 100.0 * (cur.Investigations - prev.Investigations) / prev.Investigations,
Breaches = cur.Breaches,
BreachesChange = 100.0 * (cur.Breaches - prev.Breaches) / prev.Breaches
}
)
.ToList();
I must be doing something fundamentally wrong here. I'm trying to get a "More Like This" query working in a search engine project we have that uses Elastic Search. The idea is that the CMS can write tags (like categories) to the page in a Meta tag or something, and we would read those into Elastic and use them to drive a "more like this" search based upon an input document id.
So if the input document has tags of catfish, chicken, goat I would expect Elastic Search to find other documents that share those tags and not return ones for racecar and airplane.
I've built a proof of concept console app by:
Getting a local Elastic Search 6.6.1 instance running in Docker by following the instructions on https://www.elastic.co/guide/en/elasticsearch/reference/current/docker.html
Creating a new .NET Framework 4.6.1 Console App
Adding the NuGet packages for NEST 6.5.0 and ElasticSearch.Net 6.5.0
Then I created a new elastic index that contains objects (Type "MyThing") that have a "Tags" property. This tag is a random comma-delimited set of words from a set of possible values. I've inserted anywhere from 100 to 5000 items in the index in testing. I've tried more and fewer possible words in the set.
No matter what I try the MoreLikeThis query never returns anything, and I don't understand why.
Query that isn't returning results:
var result = EsClient.Search<MyThing>(s => s
.Index(DEFAULT_INDEX)
.Query(esQuery =>
{
var mainQuery = esQuery
.MoreLikeThis(mlt => mlt
.Include(true)
.Fields(f => f.Field(ff => ff.Tags, 5))
.Like(l => l.Document(d => d.Id(id)))
);
return mainQuery;
}
Full "program.cs" source:
using Nest;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Test_MoreLikeThis_ES6
{
class Program
{
public class MyThing
{
public string Tags { get; set; }
}
const string ELASTIC_SERVER = "http://localhost:9200";
const string DEFAULT_INDEX = "my_index";
const int NUM_RECORDS = 1000;
private static Uri es_node = new Uri(ELASTIC_SERVER);
private static ConnectionSettings settings = new ConnectionSettings(es_node).DefaultIndex(DEFAULT_INDEX);
private static ElasticClient EsClient = new ElasticClient(settings);
private static Random rnd = new Random();
static void Main(string[] args)
{
Console.WriteLine("Rebuild index? (y):");
var answer = Console.ReadLine().ToLower();
if (answer == "y")
{
RebuildIndex();
for (int i = 0; i < NUM_RECORDS; i++)
{
AddToIndex();
}
}
Console.WriteLine("");
Console.WriteLine("Getting a Thing...");
var aThingId = GetARandomThingId();
Console.WriteLine("");
Console.WriteLine("Looking for something similar to document with id " + aThingId);
Console.WriteLine("");
Console.WriteLine("");
GetMoreLikeAThing(aThingId);
}
private static string GetARandomThingId()
{
var firstdocQuery = EsClient
.Search<MyThing>(s =>
s.Size(1)
.Query(q => {
return q.FunctionScore(fs => fs.Functions(fn => fn.RandomScore(rs => rs.Seed(DateTime.Now.Ticks).Field("_seq_no"))));
})
);
if (!firstdocQuery.IsValid || firstdocQuery.Hits.Count == 0) return null;
var hit = firstdocQuery.Hits.First();
Console.WriteLine("Found a thing with id '" + hit.Id + "' and tags: " + hit.Source.Tags);
return hit.Id;
}
private static void GetMoreLikeAThing(string id)
{
var result = EsClient.Search<MyThing>(s => s
.Index(DEFAULT_INDEX)
.Query(esQuery =>
{
var mainQuery = esQuery
.MoreLikeThis(mlt => mlt
.Include(true)
.Fields(f => f.Field(ff => ff.Tags, 5))
.Like(l => l.Document(d => d.Id(id)))
);
return mainQuery;
}
));
if (result.IsValid)
{
if (result.Hits.Count > 0)
{
Console.WriteLine("These things are similar:");
foreach (var hit in result.Hits)
{
Console.WriteLine(" " + hit.Id + " : " + hit.Source.Tags);
}
}
else
{
Console.WriteLine("No similar things found.");
}
}
else
{
Console.WriteLine("There was an error running the ES query.");
}
Console.WriteLine("");
Console.WriteLine("Enter (y) to get another thing, or anything else to exit");
var y = Console.ReadLine().ToLower();
if (y == "y")
{
var aThingId = GetARandomThingId();
GetMoreLikeAThing(aThingId);
}
Console.WriteLine("");
Console.WriteLine("Any key to exit...");
Console.ReadKey();
}
private static void RebuildIndex()
{
var existsResponse = EsClient.IndexExists(DEFAULT_INDEX);
if (existsResponse.Exists) //delete existing mapping (and data)
{
EsClient.DeleteIndex(DEFAULT_INDEX);
}
var rebuildResponse = EsClient.CreateIndex(DEFAULT_INDEX, c => c.Settings(s => s.NumberOfReplicas(1).NumberOfShards(5)));
var response2 = EsClient.Map<MyThing>(m => m.AutoMap());
}
private static void AddToIndex()
{
var myThing = new MyThing();
var tags = new List<string> {
"catfish",
"tractor",
"racecar",
"airplane",
"chicken",
"goat",
"pig",
"horse",
"goose",
"duck"
};
var randNum = rnd.Next(0, tags.Count);
//get randNum random tags
var rand = tags.OrderBy(o => Guid.NewGuid().ToString()).Take(randNum);
myThing.Tags = string.Join(", ", rand);
var ir = new IndexRequest<MyThing>(myThing);
var indexResponse = EsClient.Index(ir);
Console.WriteLine("Index response: " + indexResponse.Id + " : " + string.Join(" " , myThing.Tags));
}
}
}
The issue here is that the default min_term_freq value of 2 will never be satisfied for any of the terms of the prototype document because all documents contain only each tag (term) once. If you drop min_term_freq to 1, you'll get results. Might also want to set min_doc_freq to 1 too, and combine with a query that excludes the prototype document.
Here's an example to play with
const string ELASTIC_SERVER = "http://localhost:9200";
const string DEFAULT_INDEX = "my_index";
const int NUM_RECORDS = 1000;
private static readonly Random _random = new Random();
private static readonly IReadOnlyList<string> Tags =
new List<string>
{
"catfish",
"tractor",
"racecar",
"airplane",
"chicken",
"goat",
"pig",
"horse",
"goose",
"duck"
};
private static ElasticClient _client;
private static void Main()
{
var pool = new SingleNodeConnectionPool(new Uri(ELASTIC_SERVER));
var settings = new ConnectionSettings(pool)
.DefaultIndex(DEFAULT_INDEX);
_client = new ElasticClient(settings);
Console.WriteLine("Rebuild index? (y):");
var answer = Console.ReadLine().ToLower();
if (answer == "y")
{
RebuildIndex();
AddToIndex();
}
Console.WriteLine();
Console.WriteLine("Getting a Thing...");
var aThingId = GetARandomThingId();
Console.WriteLine();
Console.WriteLine("Looking for something similar to document with id " + aThingId);
Console.WriteLine();
Console.WriteLine();
GetMoreLikeAThing(aThingId);
}
public class MyThing
{
public List<string> Tags { get; set; }
}
private static string GetARandomThingId()
{
var firstdocQuery = _client
.Search<MyThing>(s =>
s.Size(1)
.Query(q => q
.FunctionScore(fs => fs
.Functions(fn => fn
.RandomScore(rs => rs
.Seed(DateTime.Now.Ticks)
.Field("_seq_no")
)
)
)
)
);
if (!firstdocQuery.IsValid || firstdocQuery.Hits.Count == 0) return null;
var hit = firstdocQuery.Hits.First();
Console.WriteLine($"Found a thing with id '{hit.Id}' and tags: {string.Join(", ", hit.Source.Tags)}");
return hit.Id;
}
private static void GetMoreLikeAThing(string id)
{
var result = _client.Search<MyThing>(s => s
.Index(DEFAULT_INDEX)
.Query(esQuery => esQuery
.MoreLikeThis(mlt => mlt
.Include(true)
.Fields(f => f.Field(ff => ff.Tags))
.Like(l => l.Document(d => d.Id(id)))
.MinTermFrequency(1)
.MinDocumentFrequency(1)
) && !esQuery
.Ids(ids => ids
.Values(id)
)
)
);
if (result.IsValid)
{
if (result.Hits.Count > 0)
{
Console.WriteLine("These things are similar:");
foreach (var hit in result.Hits)
{
Console.WriteLine($" {hit.Id}: {string.Join(", ", hit.Source.Tags)}");
}
}
else
{
Console.WriteLine("No similar things found.");
}
}
else
{
Console.WriteLine("There was an error running the ES query.");
}
Console.WriteLine();
Console.WriteLine("Enter (y) to get another thing, or anything else to exit");
var y = Console.ReadLine().ToLower();
if (y == "y")
{
var aThingId = GetARandomThingId();
GetMoreLikeAThing(aThingId);
}
Console.WriteLine();
Console.WriteLine("Any key to exit...");
}
private static void RebuildIndex()
{
var existsResponse = _client.IndexExists(DEFAULT_INDEX);
if (existsResponse.Exists) //delete existing mapping (and data)
{
_client.DeleteIndex(DEFAULT_INDEX);
}
var rebuildResponse = _client.CreateIndex(DEFAULT_INDEX, c => c
.Settings(s => s
.NumberOfShards(1)
)
.Mappings(m => m
.Map<MyThing>(mm => mm.AutoMap())
)
);
}
private static void AddToIndex()
{
var bulkAllObservable = _client.BulkAll(GetMyThings(), b => b
.RefreshOnCompleted()
.Size(1000));
var waitHandle = new ManualResetEvent(false);
Exception exception = null;
var bulkAllObserver = new BulkAllObserver(
onNext: r =>
{
Console.WriteLine($"Indexed page {r.Page}");
},
onError: e =>
{
exception = e;
waitHandle.Set();
},
onCompleted: () => waitHandle.Set());
bulkAllObservable.Subscribe(bulkAllObserver);
waitHandle.WaitOne();
if (exception != null)
{
throw exception;
}
}
private static IEnumerable<MyThing> GetMyThings()
{
for (int i = 0; i < NUM_RECORDS; i++)
{
var randomTags = Tags.OrderBy(o => Guid.NewGuid().ToString())
.Take(_random.Next(0, Tags.Count))
.OrderBy(t => t)
.ToList();
yield return new MyThing { Tags = randomTags };
}
}
And here's an example output
Found a thing with id 'Ugg9LGkBPK3n91HQD1d5' and tags: airplane, goat
These things are similar:
4wg9LGkBPK3n91HQD1l5: airplane, goat
9Ag9LGkBPK3n91HQD1l5: airplane, goat
Vgg9LGkBPK3n91HQD1d5: airplane, goat, goose
sQg9LGkBPK3n91HQD1d5: airplane, duck, goat
lQg9LGkBPK3n91HQD1h5: airplane, catfish, goat
9gg9LGkBPK3n91HQD1l5: airplane, catfish, goat
FQg9LGkBPK3n91HQD1p5: airplane, goat, goose
Jwg9LGkBPK3n91HQD1p5: airplane, goat, goose
Fwg9LGkBPK3n91HQD1d5: airplane, duck, goat, tractor
Kwg9LGkBPK3n91HQD1d5: airplane, goat, goose, horse
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My current code is like this:
var results = new List<Results>();
var items = new List<string>
{
"B,0",
"A,1",
"B,2",
"A,3",
"A,4",
"B,5",
"A,6",
"A,7",
"B,8"
};
int size = 2;
int temp;
var tempResults = new List<int>();
var keys = items.Select(t => t.Split(',')[0]).Distinct().ToList();
//var values = items.Select(t => t.Split(',')[1]).ToList();
//var result = items.SelectMany(k => values, (k, v) => new {k, v});
foreach (var key in keys)
{
temp = 0;
tempResults = new List<int>();
foreach (var item in items)
{
if (item.Split(',')[0] == key)
{
tempResults.Add(Int32.Parse(item.Split(',')[1]));
temp++;
}
if (temp == size)
{
results.Add(new Results
{
Key = key,
Values = new List<int>(tempResults)
});
temp = 0;
tempResults.Clear();
}
}
}
foreach (Results r in results)
{
Console.WriteLine("Key: " + r.Key);
Console.WriteLine("Values: ");
foreach (int i in r.Values)
{
Console.WriteLine(i);
}
}
Everything works fine with it, but I am using two loops to get the results needed. I want to replace them with a LINQ expression and been trying, but can't seem to figure it out. Any help is appreciated.
You could use a combination of LINQ methods: .GroupBy, .Select, SelectMany and some data structures like Tuple<T1, T2>.
Provided that we have class:
class Results
{
public string Key { get; set; }
public List<int> Values { get; set; }
}
The solution could be:
int k = 0;
var result =
items.Select(x => // parse initial string
{
var strValue = x.Split(',');
return Tuple.Create(strValue[0], Convert.ToInt32(strValue[1]));
})
.GroupBy(x => x.Item1, y => y.Item2) // group by key
.Select(x => Tuple.Create(x.Key, x)) // flatten to IEnumerable
.SelectMany(x => // select fixed size data chunks
x.Item2.GroupBy(y => k++ / size, z => z)
.Select(z => Tuple.Create(x.Item1, z)))
.Select(x => // cast to resulting model type
new Results()
{
Key = x.Item1,
Values = x.Item2.ToList()
})
.ToList(); // Return enumeration as list
How about writing a couple extension methods?
const int partitionSize = 2;
var itemLookup = items.ToLookup(x => x.Split(',')[0], x => Int32.Parse(x.Split(',')[1]));
var partitionedItems = itemLookup.Partition(partitionSize);
foreach (var partition in partitionedItems)
foreach (var lookup in partition)
{
Console.WriteLine("Key: " + lookup.Key);
Console.WriteLine("Values: ");
foreach (var i in lookup.ToList())
{
Console.WriteLine(i);
}
}
public static class PartitionExtensions
{
public static IList<ILookup<K, V>> Partition<K, V>(this ILookup<K, V> lookup, int size)
{
return lookup.SelectMany(l => l.ToList().Partition(size).Select(p => p.ToLookup(x => l.Key, x => x))).ToList();
}
public static IList<IList<T>> Partition<T>(this IList<T> list, int size)
{
IList<IList<T>> results = new List<IList<T>>();
var itemCount = list.Count();
var partitionCount = itemCount / size;
//your paritioning method is truncating items that don't make up a full partition
//if you want the remaining items in a partial partition, use this code instead
//var partitionCount = ((itemCount % size == 0) ? itemCount : itemCount + size) / size;
for (var i = 0; i < partitionCount; i++)
{
results.Add(list.Skip(i * size).Take(size).ToList());
}
return results;
}
}
Not really a way to remove the inner loop, but you could shorten a bit your code with:
....
var keys = items.Select(t => t.Split(',')[0]).Distinct().ToList();
foreach (var key in keys)
{
var forKey = items.Where(x => x.Split(',')[0] == key)
.Select(k => int.Parse(k.Split(',')[1]));
for (int x = 0; x < forKey.Count(); x += size)
{
results.Add(new Results
{
Key = key,
Values = forKey.Skip(x).Take(size).ToList()
});
}
}
....
At least this approach will remove the need of the temporary variables and all the if checks inside the loop and will also include in your results the last value for the A key that has only one integer in its list.
How can I write an algorithm that can take unused ID's out of a sequence starting from 1 to 99 in the format "C00"? For example NewId(['C01', 'C02', 'C03']) should emit 'C04', but NewId(['C02', 'C03', 'C04']) should emit C01, and NewId(['C01', 'C03', 'C04']) should result in C02.
I wrote an implementation but the result is wrong.
Example : CAT_ID : C01, C02, C05, C06, C11. When I run it, the expected result is C03. My algorithm is as follows:
Sort ID asc
Go through every item in the list
Compare first value with the next, if they are not the same, add 1 and exit loop.
This is my code:
public static string Get_AreaID_Auto()
{
string result = "";
if (db.TESTs.ToList().Count <= 0)
{
result = "01";
}
else
{
int maxId = 0;
foreach (var item in db.TESTs.OrderBy(e => e.CAT_ID).ToList())
{
if (int.Parse(item.CAT_ID.Substring(1)) + 1 != int.Parse(item.CAT_ID.Substring(1)))
{
maxId = int.Parse(item.CAT_ID.Substring(1) + 1);
break;
}
}
switch (maxId.ToString().Length)
{
case 1:
if (maxId == 9)
{
result = "10";
}
else
result = "0" + (maxId + 1);
break;
case 2:
result = "" + (maxId + 1);
break;
default:
break;
}
}
return "C" + result;
}
Can someone point out what is wrong?
This should work for you:
public static string Get_AreaID_Auto()
{
var existing = db.TESTs.Select(e => e.CAT_ID).OrderBy(x => x).ToList();
if (existing.Count == 0)
{
return "C01";
}
else
{
return
existing
.Concat(new [] { "" })
.Select((x, n) => new
{
actual = x,
expected = String.Format("C{0:00}", n + 1),
})
.Where(x => x.actual != x.expected)
.Select(x => x.expected)
.First();
}
}
This uses a generate and test approach. No parsing necessary.
I just realised with the .Concat(new [] { "" }) change that the if statement is now no longer required. You can do this instead:
public static string Get_AreaID_Auto()
{
return
db.TESTs
.Select(e => e.CAT_ID)
.OrderBy(x => x)
.ToArray()
.Concat(new [] { "" })
.Select((x, n) => new
{
actual = x,
expected = String.Format("C{0:00}", n + 1),
})
.Where(x => x.actual != x.expected)
.Select(x => x.expected)
.First();
}
Try this
public static string Get_AreaID_Auto()
{
string result = "";
if (db.TESTs.ToList().Count <= 0)
{
result = "01";
}
else
{
var item = db.TESTs.OrderByDescending(e => e.CAT_ID).First();
result = int.Parse(item.CAT_ID.Substring(1)) + 1;
}
return string.Format("C{0:D3}",result);
}
Updated Code...Now Try this
public static string Get_AreaID_Auto()
{
string result = "";
if (db.TESTs.ToList().Count <= 0)
{
result = "01";
}
else
{
var items = db.TESTs.OrderBy(e => e.CAT_ID).ToArray();
for(int i=0;i<items.count;i++)
{
if ((i==items.count-1) || (int.Parse(items[i].CAT_ID.Substring(1)) + 1 != int.Parse(items[i+1].CAT_ID.Substring(1))))
{
result = int.Parse(items[i].CAT_ID.Substring(1) + 1);
break;
}
}
}
return string.Format("C{0:D2}",result);
}
Here is a solution I think would work:
var items = db.TESTs.Select(x => int.Parse(x.CAT_ID.Substring(1))).OrderBy(v => v).ToArray();
if(!items.Any())
return "C01";
int current = 0;
for (int i = 0; i < items.Length; i++)
{
if (items[i] > current + 1)
return "C" + (current + 1) .ToString("00");
current = items[i];
}
return "C" + (items.Max() + 1).ToString("00");
I have a dictionary containg ID which are alphanumeric (e.g. a10a10 & d10a9) from which I want the biggest ID, meaning 9 < 10 < a ...
When I use the following code, d10a9 is MAX since 9 is sorted before 10
var lsd = new Dictionary<string, string>();
lsd.Add("a", "d10a10");
lsd.Add("b", "d10a9");
string max = lsd.Max(kvp => kvp.Value);
How can I get the Max value of the IDs with the Longest string combined?
I think you may try to roll your own IComparer<string>
class HumanSortComparer : IComparer<string>
{
public int Compare(string x, string y)
{
// your human sorting logic here
}
}
Usage:
var last = collection.OrderBy(x => x.Value, new HumanSortComparer()).LastOrDefault();
if (last != null)
string max = last.Value;
this works like a charm assuming IDs always start with "d10a":
int max = lsd.Max(kvp => Convert.ToInt32(kvp.Value.Substring(4)));
Console.Write(string.Format("d10a{0}", max));
One way would be to do this
string max =lsd.Where(kvp=>kvp.Value.Length==lsd.Max(k=>k.Value.Length)).Max(kvp => kvp.Value);
however I think that this method would evalute the max length for each item so you may be better to extract it to a variable first
int maxLength=lsd.Max(kvp=>kvp.Value.Length);
string max = lsd.Where(kvp=>kvp.Value.Length == maxLength).Max(kvp => kvp.Value);
If you are going to have null strings in there you may need to perform null checks too
int maxLength=lsd.Max(kvp=>(kvp.Value??String.Empty).Length);
string max = lsd.Where(kvp=>(kvp.Value??String.Empty).Length == maxLength).Max(kvp => kvp.Value);
Alternatively treat your string as Base36 number and convert to long for the max function and then convert back again to get the max string.
string max =lsd.Max(tvp=>tvp.Value.FromBase36()).ToBase36();
public static class Base36 {
public static long FromBase36(this string src) {
return src.ToLower().Select(x=>(int)x<58 ? x-48 : x-87).Aggregate(0L,(s,x)=>s*36+x);
}
public static string ToBase36(this long src) {
StringBuilder result=new StringBuilder();
while(src>0) {
var digit=(int)(src % 36);
digit=(digit<10) ? digit+48 :digit+87;
result.Insert(0,(char)digit);
src=src / 36;
}
return result.ToString();
}
}
Finally just just the Agregate extension method instead of Max as this lets you do all the comparison logic....
lsd.Agregate(string.Empty,(a,b)=> a.Length == b.Length ? (a>b ? a:b) : (a.Length>b.Length ? a:b));
This could doesn't have null checks but you easily add them in.
I think if you did this:
var max = lsd.OrderByDescending(x => x.Value)
.GroupBy(x => x.Value.Length)
.OrderByDescending(x => x.Key)
.SelectMany(x => x)
.FirstOrDefault();
It may give you what you want.
You need StringComparer.OrdinalIgnoreCase.
Without the need to use linq, the function that do that is quite simple.
Complexity is, of course, O(n).
public static KeyValuePair<string, string> FindMax(IEnumerable<KeyValuePair<string, string>> lsd)
{
var comparer = StringComparer.OrdinalIgnoreCase;
var best = default(KeyValuePair<string, string>);
bool isFirst = true;
foreach (KeyValuePair<string, string> kvp in lsd)
{
if (isFirst || comparer.Compare(kvp.Value, best.Value) > 0)
{
isFirst = false;
best = kvp;
}
}
return best;
}
Okay - I think you need to first turn each key into a series of strings and numbers - since you need the whole number to be able to determine the comparison. Then you implement an IComparer - I've tested this with your two input strings as well as with a few others and it appears to do what you want. The performance could possibly be improved - but I was brainstorming it!
Create this class:
public class ValueChain
{
public readonly IEnumerable<object> Values;
public int ValueCount = 0;
private static readonly Regex _rx =
new Regex("((?<alpha>[a-z]+)|(?<numeric>([0-9]+)))",
RegexOptions.Compiled | RegexOptions.IgnoreCase);
public ValueChain(string valueString)
{
Values = Parse(valueString);
}
private IEnumerable<object> Parse(string valueString)
{
var matches = _rx.Matches(valueString);
ValueCount = matches.Count;
foreach (var match in matches.Cast<Match>())
{
if (match.Groups["alpha"].Success)
yield return match.Groups["alpha"].Value;
else if (match.Groups["numeric"].Success)
yield return int.Parse(match.Groups["numeric"].Value);
}
}
}
Now this comparer:
public class ValueChainComparer : IComparer<ValueChain>
{
private IComparer<string> StringComparer;
public ValueChainComparer()
: this(global::System.StringComparer.OrdinalIgnoreCase)
{
}
public ValueChainComparer(IComparer<string> stringComparer)
{
StringComparer = stringComparer;
}
#region IComparer<ValueChain> Members
public int Compare(ValueChain x, ValueChain y)
{
//todo: null checks
int comparison = 0;
foreach (var pair in x.Values.Zip
(y.Values, (xVal, yVal) => new { XVal = xVal, YVal = yVal }))
{
//types match?
if (pair.XVal.GetType().Equals(pair.YVal.GetType()))
{
if (pair.XVal is string)
comparison = StringComparer.Compare(
(string)pair.XVal, (string)pair.YVal);
else if (pair.XVal is int) //unboxing here - could be changed
comparison = Comparer<int>.Default.Compare(
(int)pair.XVal, (int)pair.YVal);
if (comparison != 0)
return comparison;
}
else //according to your rules strings are always greater than numbers.
{
if (pair.XVal is string)
return 1;
else
return -1;
}
}
if (comparison == 0) //ah yes, but were they the same length?
{
//whichever one has the most values is greater
return x.ValueCount == y.ValueCount ?
0 : x.ValueCount < y.ValueCount ? -1 : 1;
}
return comparison;
}
#endregion
}
Now you can get the max using OrderByDescending on an IEnumerable<ValueChain> and FirstOrDefault:
[TestMethod]
public void TestMethod1()
{
List<ValueChain> values = new List<ValueChain>(new []
{
new ValueChain("d10a9"),
new ValueChain("d10a10")
});
ValueChain max =
values.OrderByDescending(v => v, new ValueChainComparer()).FirstOrDefault();
}
So you can use this to sort the string values in your dictionary:
var maxKvp = lsd.OrderByDescending(kvp => new ValueChain(kvp.Value),
new ValueChainComparer()).FirstOrDefault();