I have a list like this:
item.Add("a");
item.Add("as");
item.Add("b");
item.Add("fgs");
item.Add("adsd");
How can I find all items that start with (for example) "a"?
This "a" is not some hardcoded string, so I will need a function that do this for each string.
I try with FindAll, but I did not figured out how it works.
Br, Wolfy
If by "start with" you mean the first char, then:
item.FindAll(i => i[0] == 'a');
if you mean a string (may be other than 1 char) then:
item.FindAll(i => i.StartsWith("a"));
If you want a different comparison, such as case-insensitive, locale-based, etc. then do the relevant IndexOf such as:
item.FindAll(i => i.IndexOf("a", StringComparison.CurrentCultureIgnoreCase) == 0);
All of the above can be easily adapted to be use a relevant char or string variable or parameter.
If you don't need the extra properties and methods provided by a list, then it will be more efficient to use Where than FindAll as FindAll creates a new list, and does so in all at once, while Where will enumerate the matching results as it is iterated through.
Or with LINQ
from i in items where i.StartsWith("a") select i;
for NET2.0 you may use this method:
'pattern' is an argument to look for (f.e. "a")
private List<string> FindAll(List<string> list, string pattern)
{ // returns found results
return list.FindAll(delegate(string item)
{
return item.StartsWith(pattern);
});
}
I thought you have another list that contains the startswith criteria strings. Lets call your items "words" and the other list "keywords". So the below query will return what you want.
List<string> words = new List<string>();
words.Add("a");
words.Add("as");
words.Add("b");
words.Add("fgs");
words.Add("adsd");
List<string> keywords = new List<string>();
keywords.Add("a");
keywords.Add("b");
var result = words.FindAll(o =>
keywords.Any(a => o.StartsWith(a))
);
This result has the words that starts with any of the keyword from keywords.
List<string> item = new List<string>();
item.Add("a");
item.Add("as");
item.Add("b");
item.Add("fgs");
item.Add("adsd");
var res1 = item.FindAll(i => i.StartsWith("a"));
var res2 = item.Where(i => i.StartsWith("a"));
Try this
item.FindAll(i => i.Contains("a"));
This will return a List containting only the filtered strings.
Related
Given a List<string> How to return all records in an entity that has a field containing one or more words from the list.
I tried the below which does not work and I'm starting to go around in circles a bit:
List<string> searchwords = new List<string>() {"word1","word2"};
var results = context.activities
.Where(a => a.Title.Contains(searchwords.Any().ToString())).ToList();
The problem with your current code:
var results = context.activities.Where(a =>
a.Title.Contains(searchwords.Any().ToString())).ToList();
is that you have your needle and haystack backwards. The fact that you needed to call .ToString() on Any() should have tipped you off. Any() returns a bool, which you're casting to a string, so you're just checking whether Title contains the string "True". Definitely not what you want. You want something closer to:
var results = context.activities
.Where(a => searchwords.Any(searchWord => a.Title.Contains(searchWord)));
In C#, I know how to use Regex.Replace a Linq query to replace substrings within an input string, as shown in this code sample.
var standards = _db.MapsFromOws.AsEnumerable().Select(m =>
m.Section).Distinct().AsEnumerable();
var enumerable = standards as IList<string> ?? standards.ToList();
const string elaPattern1 = #"LA.\d{1,2}-\d{1,2}.(\d{1,2}).([A-z]{1,2}).(\d{1,2})";
const string elaReplace1 = "$1.$2.$3";
var ela1 = enumerable
.AsEnumerable()
.Select(
m =>
new TranslationSelectModel
{
Section = m,
/* If m is a match to elaPattern1 then replace else m*/
Translation = Regex.Replace(m, elaPattern1, elaReplace1)
})
.OrderBy(m => m.Section).AsEnumerable();
This works well if there is only one pattern I need to replace, but what if I have to apply a set of pattern-replacements in the same list?
I had an idea of using a Dictionary<string,string> as a source of Regex patterns and replacement string. For example,
var regexPatternDictionary = new Dictionary<string, string>()
{
{#"LA.\d{1,2}-\d{1,2}.(\d{1,2}).([A-z]{1,2}).(\d{1,2})","$1.$2.$3"},
{#"MA.9-12.HS.([A-z])-([A-z]{0,3}).([A-z]).(\d)(.[A-z])*","HS.$1-$2.$3.$4$5"}
};
My question is how I would be able to use Regex.Replace() so that it matches each item in the enumerable to the regular expression dictionary instead of a single string variable?
The algorithm I'm seeing in my mind is:
For each item in enumerable
If item is a match to a dictionary, then apply replacement
Loop to next item
Not sure if I understand your problem 100%, but try something like this:
var result = enumerable.Select(x => replaceDictionary
.Aggregate(x, (y,z) => Regex.Replace(y, z.Key, z.Value))
.ToArray()
I have a List of strings with the items such-
Titanic, Leonardo Decaprio
Mission Impossible, Tom Cruise
Is there any way such that I can get only the first substring before the comma? In above case the expected output for List<string> should be -
Titanic
Mission Impossible
You can use Split method and then using Select method get only the first part.
list.Select(x=> x.Split(',')[0]);
You can use Substring and IndexOf instead of Split
list.Select(x => x.Substring(0, x.IndexOf(',')));
If you are not sure that every string contains comma you can check it, for example this way
list.Select(x => x.Substring(0, x.IndexOf(',') > 0 ? x.IndexOf(',') : x.Length))
You will also need to call .ToList() method otherwise it will not cast the resulting list into List<string> and throw exception because resulting list would of type System.Collections.Generic.IEnumerable<string> and your's is of List<string
List<string> list = new List<string>() { "Titanic, Leonardo Decaprio", " Mission Impossible, Tom Cruise" };
list = list.Select(x => x.Split(',')[0]).ToList();
Hello I have these two Lists
List<string> list1 = {"404a49ad-d80f-4ef7-99ab-0996de3b70d4_29190_806.jpg|Name1", "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29197_806.jpg|Name2", "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29210_868.jpg|Name3"}
List<string> list2 = {"404a49ad-d80f-4ef7-99ab-0996de3b70d4_29190_806.jpg","404a49ad-d80f-4ef7-99ab-0996de3b70d4_29197_806.jpg"}
I want to intersect the values of list1 separating by '|' character, with the list2 values, but I want to return the full string of list1 and not only the first part separated by '|' character.
This is the result i want:
var finalList = {"404a49ad-d80f-4ef7-99ab-0996de3b70d4_29190_806.jpg|Name1", "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29197_806.jpg|Name2"}
I dont know if its possible with the instersect function or there is another approach I can use. I've tried using Contains function in a predicate but it takes to much time to find the matches.
I'm using large lists with 2000 elements approx.
Thanks!
Try this, gives the expected results in LinqPad, using your example:
var intersection =
list1.Join(
list2,
l1 => l1.Split('|')[0], //Selector for items from the inner list splits on '|'
l2 => l2, //Select the current item
(l1, l2) => l1);
Compile list2 into a HashSet<string> to allow fast lookups. Then, use a simple Where filter to perform lookups of substrings from list1 against this set.
List<string> list1 = new List<string> { "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29190_806.jpg|Name1", "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29197_806.jpg|Name2", "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29210_868.jpg|Name3" };
List<string> list2 = new List<string> { "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29190_806.jpg", "404a49ad-d80f-4ef7-99ab-0996de3b70d4_29197_806.jpg" };
var list2HashSet = new HashSet<string>(list2);
var finalList = list1.Where(s => list2HashSet.Contains(s.Substring(0, s.IndexOf('|')))).ToList();
Note that s.Substring(0, s.IndexOf('|')) is semantically equivalent to s.Split('|')[0] (assuming that all your strings contain |), but avoids the overhead of allocating another string instance for the text behind the |.
Use where to iterate over the list. Use the Split method to get the first part you are interested in, and then check to see if list2 contains that string. Finally call ToList to convert the result to a list.
var finalList = list1.Where(x => list2.Contains(x.Split(new []{'|'})[0})).ToList();
I have an text document of emails such as
Google12#gmail.com,
MyUSERNAME#me.com,
ME#you.com,
ratonabat#co.co,
iamcool#asd.com,
ratonabat#co.co,
I need to check said document for duplicates and create a unique array from that (so if "ratonabat#co.co" appears 500 times in the new array he'll only appear once.)
Edit:
For an example:
username1#hotmail.com
username2#hotmail.com
username1#hotmail.com
username1#hotmail.com
username1#hotmail.com
username1#hotmail.com
This is my "data" (either in an array or text document, I can handle that)
I want to be able to see if there's a duplicate in that, and move the duplicate ONCE to another array. So the output would be
username1#hotmail.com
You can simply use Linq's Distinct extension method:
var input = new string[] { ... };
var output = input.Distinct().ToArray();
You may also want to consider refactoring your code to use a HashSet<string> instead of a simple array, as it will gracefully handle duplicates.
To get an array containing only those records which are duplicates, it's a little moe complex, but you can still do it with a little Linq:
var output = input.GroupBy(x => x)
.Where(g => g.Skip(1).Any())
.Select(g => g.Key)
.ToArray();
Explanation:
.GroupBy group identical strings together
.Where filter the groups by the following criteria
.Skip(1).Any() return true if there are 2 or more items in the group. This is equivalent to .Count() > 1, but it's slightly more efficient because it stops counting after it finds a second item.
.Select return a set consisting only of a single string (rather than the group)
.ToArray convert the result set to an array.
Here's another solution using a custom extension method:
public static class MyExtensions
{
public static IEnumerable<T> Duplicates<T>(this IEnumerable<T> input)
{
var a = new HashSet<T>();
var b = new HashSet<T>();
foreach(var x in input)
{
if (!a.Add(x) && b.Add(x))
yield return x;
}
}
}
And then you can call this method like this:
var output = input.Duplicates().ToArray();
I haven't benchmarked this, but it should be more efficient than the previous method.
You can use the built in in .Distinct() method, by default the comparisons are case sensitive, if you want to make it case insenstive use the overload that takes a comparer in and use a case insensitive string comparer.
List<string> emailAddresses = GetListOfEmailAddresses();
string[] uniqueEmailAddresses = emailAddresses.Distinct(StringComparer.OrdinalIgnoreCase).ToArray();
EDIT: Now I see after you made your clarification you only want to list the duplicates.
string[] duplicateAddresses = emailAddresses.GroupBy(address => address,
(key, rows) => new {Key = key, Count = rows.Count()},
StringComparer.OrdinalIgnoreCase)
.Where(row => row.Count > 1)
.Select(row => row.Key)
.ToArray();
To select emails which occur more then once..
var dupEmails=from emails in File.ReadAllText(path).Split(',').GroupBy(x=>x)
where emails.Count()>1
select emails.Key;