I have a collection. And in this collection, if a duplicate is added, I want to append the text " - N" (Where N is an integer that is not used by a current item in the collection).
For Example, if I have the following list:
item1
item2
and try to add 'item1' again, I want the list to end up like so:
item1
item2
item1 - 1
If I try to add 'item1' again, the list will then be:
item1
item2
item1 - 1
item1 - 2
Pretty straight forward. Below is my simple algorithm, but I'm getting a noticeable loss in performance when dealing with 10,000 items. Obviously that's going to happen somewhat, but are there better approaches to this? Couldn't find any similar question asked, so figure I'd see if anyone has ran into a similar issue.
Item copyItem = new Item();
string tempName = name;
int copyNumber = 1;
while(copyItem != null)
{
copyItem = MyCollection.FirstOrDefault(blah => blah.Name == tempName);
if (copyItem == null)
{
name = tempName;
break;
}
tempName = name + " - " + copyNumber;
++copyNumber;
}
I would firstly sort the values - thanks to this you only need to make a check with the previous value and not with the whole collection.
So it could look like this:
List<string> values = new List<string> { "item1", "item1", "item1" };
values.Sort();
string previousValue = string.Empty;
int number = 1;
for(int i = 0 ; i < values.Count; i ++)
{
if (values[i].Equals(previousValue))
{
previousValue = values[i];
values[i] = values[i] + "-" + number;
number++;
}
else
{
previousValue = values[i];
number = 1;
}
}
I would use a Dictionary<string, int> to store the number of duplicates for a particular item. So a helper method would look something like this:
Dictionary<string, int> countDictionary = new Dictionary<string, int>(); // case sensitive!
string GetNameForItem(string itemName)
{
var name = itemName;
var count = 0;
countDictionary.TryGetValue(itemName, out count);
if (count > 0)
name = string.Format("{0} - {1}", itemName, count);
countDictionary[itemName] = count + 1;
return name;
}
Alternatively, you could split up the operation into several methods if you didn't want GetNameForItem to automatically increment on retrieval:
int GetCountForItem(string itemName)
{
var count = 0;
countDictionary.TryGetValue(itemName, out count);
return count;
}
string GetNameForItem(string itemName)
{
var name = itemName;
var count = GetCountForItem(itemName);
if (count > 0)
name = string.Format("{0} - {1}", itemName, count);
return name;
}
int IncrementCountForItem(string itemName)
{
var newCount = GetCountForItem(itemName) + 1;
countDictionary[itemName] = newCount;
return newCount;
}
It is important to note that if you are supporting deletion from the collection, you will have to update the count accordingly:
int DecrementCountForItem(string itemName)
{
var newCount = Math.Max(0, GetCountForItem(itemName) - 1); // Prevent count from going negative!
countDictionary[itemName] = newCount;
return newCount;
}
You will also have to keep in mind what happens if you have two items, say "Item A" and "Item A - 1", then you delete "Item A". Should you rename "Item A - 1" to "Item A"?
Okay so you need an iterator per value and not a global one. This code will do the thing.
// Inputs for Tests purpose
List<string> values = new List<string> { "item1", "item2", "item1", "item1" };
// Result data
List<string> finalResult = new List<string>();
// 1 - Group by item value
var tempResult = from i in values
group i by i;
// We loop over all different item name
foreach (var curItem in tempResult)
{
// Thanks to the group by we know how many item with the same name exists
for (int ite = 0; ite < curItem.Count(); ite++)
{
if (ite == 0)
finalResult.Add(curItem.Key);
else
finalResult.Add(string.Format("{0} - {1}", curItem.Key, ite));
}
}
Thanks to LINQ you can reduce the amount of code, next code will do exactly the same thing and should be also quickier because I use the ToList() method so the LINQ query will not have a deferred execution.
// Inputs for Tests purpose
List<string> values = new List<string> { "item1", "item2", "item1", "item1" };
// Result data
List<string> finalResult = new List<string>();
values.GroupBy<string, string>(s1 => s1).ToList().ForEach(curItem =>
{
for (int ite = 0; ite < curItem.Count(); ite++)
{
finalResult.Add(ite == 0 ? curItem.Key : string.Format("{0} - {1}", curItem.Key, ite));
}
});
Related
List<string> lst = new List<string>() { "mahdi","arshia","amir"};
int a = 0;
var list_mian = lst[a];
for (int i = a; i <Convert.ToInt16(list_mian); i++) //Additional information: Input string was not in a correct format.
{
MessageBox.Show(lst.IndexOf(lst[0]).ToString());
}
I want to show a list item's index in a loop, for example of mahdi's index is 0 and amir's index is 2 i wanna show their index respectively in a "for" loop and i give an error that i show that in the code part
Your trying to convert an integer to a string and then use that as a range on the for loop just use .count and compare it to the name attached to that index of the list. Hope you find this useful.
public static int? findPerson(string name)
{
List<string> lst = new List<string>() { "mahdi", "arshia", "amir" };
int? result = null;
for (int i = 0; i < lst.Count; i++) //Additional information: Input string was not in a correct format.
{
if (lst[i] == name)
{
result = i;
}
}
return result;
}
static void Main(string[] args)
{
var index = findPerson("arshia");
if (index == null)
{
Console.WriteLine("PersonNotFound");
}
else {
Console.WriteLine("Index of " + index.ToString());
}
}
You can do it with IndexOf it returns the index or -1 when there is no item.
List<string> list = new List<string>() { "mahdi", "arshia", "amir" };
var indexOfAmir = list.IndexOf("amir"); // 2
var indexOfMax = list.IndexOf("max"); // -1
I want to take a list of names, add them to an array, then split that array into N groups, then display those arrays in separate textboxes in a Windows form. So far I have this, which takes the list and splits them up, but honestly, I don't think it's doing what I want it to do.
MasterList:
Johnny, Mark, Tom, Carl, Jenny, Susie, Ben, Tim, Angie
Group 1: Johnny, Mark, Angie
Group 2: Tom, Carl
Group 3: Jenny, Susie
Group 4: Ben, Tim
void addnamestoList_Click(object sender, EventArgs e)
{
if (string.IsNullOrWhiteSpace(this.studentnameTboxContent))
{
int num = (int)MessageBox.Show("No content to format.",
"Message",
MessageBoxButtons.OK,
MessageBoxIcon.Exclamation);
}
else
{
transformText();
}
}
public void transformText()
{
string[] masterList = studentnameTboxContent.Split('\n');
var split = from index in Enumerable.Range(0, masterList.Length)
group masterList[index] by index / int.Parse(groupcountTboxContent);
studentNames.Text = "";
foreach (var Array in split)
{
studentNames.AppendText(string.Join(Environment.NewLine, Array.ToArray()));
}
}
Method to randomize list:
private string[] randomizeList(string[] list)
{
Random rnd = new Random();
string[] randomList = list.OrderBy(x => rnd.Next()).ToArray();
return randomList;
}
Here's one way to do it, but it isn't very elegant. Basically calculate the group size based on the group count entered by the user, determine how many items should be in each group, and determine the number of remaining items that need to be added to the first lists (if the group cannot be evenly divided by the count).
Then, in a loop, skip the number of items you've taken so far, then take the group size number of items, and if there are still extra items that need to be added, grab them from the end of the list:
var masterList = new List<string>
{
"Johnny", "Mark", "Tom", "Carl",
"Jenny", "Susie", "Ben", "Tim", "Angie"
};
var groupCount = 4; // Entered by the user
var minGroupSize = masterList.Count / groupCount;
var extraItems = masterList.Count % groupCount;
var groupedNames = new List<List<string>>();
for (int i = 0; i < groupCount; i++)
{
groupedNames.Add(masterList.Skip(i * minGroupSize).Take(minGroupSize).ToList());
if (i < extraItems)
{
groupedNames[i].Add(masterList[masterList.Count - 1 - i]);
}
}
Console.WriteLine("Here are the groups:");
for(int index = 0; index < groupedNames.Count; index++)
{
Console.WriteLine($"#{index + 1}: {string.Join(", ", groupedNames[index])}");
}
Console.Write("\nDone!\nPress any key to exit...");
Console.ReadKey();
Output
This code can easily be extracted into a method so it can be re-used elsewhere:
static List<List<string>> GetGroups(List<string> masterList, int groupCount)
{
var groups = new List<List<string>>();
// Argument validation. All of these conditions should be true.
if (masterList != null && groupCount > 0 && groupCount <= masterList.Count)
{
var minGroupSize = masterList.Count / groupCount;
var extraItems = masterList.Count % groupCount;
for (int i = 0; i < groupCount; i++)
{
groups.Add(masterList.Skip(i * minGroupSize).Take(minGroupSize).ToList());
if (i < extraItems)
{
groups[i].Add(masterList[masterList.Count - 1 - i]);
}
}
}
return groups;
}
Usage
var masterList = new List<string>
{
"Johnny", "Mark", "Tom", "Carl", "Jenny",
"Susie", "Ben", "Tim", "Angie"
};
var groupedNames = GetGroups(masterList, 4);
I'm trying to test a form by submitting a combination of all values to see if it breaks. These are ComboBoxes that I have stored in an ExtraField class
public class ExtraField
{
public String Name = ""; //name of form key
public Dictionary<String, String> Options = new Dictionary<String, String>(); //Format: OptionText, Value
}
I have generated a list of these fields
List<ExtraField> efList = new List<ExtraField>();
I was thinking all possible combinations of these fields could be added to a string list that I can parse (I was thinking name=opt|name=opt|name=opt). I've provided an example of what would work below (where ExtraField list Count==3):
List<ExtraField> efList = new List<ExtraField>();
ExtraField f1 = new ExtraField();
f1.Name = "name1";
f1.Options.Add("text", "option1");
f1.Options.Add("text2", "option2");
f1.Options.Add("text3", "option3");
efList.Add(f1);
ExtraField f2 = new ExtraField();
f2.Name = "name2";
f2.Options.Add("text", "option1");
f2.Options.Add("text2", "option2");
f2.Options.Add("text3", "option3");
f2.Options.Add("text4", "option4");
efList.Add(f2);
ExtraField f3 = new ExtraField();
f3.Name = "name3";
f3.Options.Add("text2", "option1");
f3.Options.Add("text3", "option2");
f3.Options.Add("text4", "option3");
f3.Options.Add("text5", "option4");
f3.Options.Add("text6", "option5");
efList.Add(f3);
Should produce
name1=option1|name2=option1|name3=option1
name1=option1|name2=option1|name3=option2
name1=option1|name2=option1|name3=option3
name1=option1|name2=option1|name3=option4
name1=option1|name2=option1|name3=option5
name1=option1|name2=option2|name3=option1
name1=option1|name2=option2|name3=option2
name1=option1|name2=option2|name3=option3
name1=option1|name2=option2|name3=option4
name1=option1|name2=option2|name3=option5
name1=option1|name2=option3|name3=option1
name1=option1|name2=option3|name3=option2
name1=option1|name2=option3|name3=option3
name1=option1|name2=option3|name3=option4
name1=option1|name2=option3|name3=option5
name1=option1|name2=option4|name3=option1
name1=option1|name2=option4|name3=option2
name1=option1|name2=option4|name3=option3
name1=option1|name2=option4|name3=option4
name1=option1|name2=option4|name3=option5
name1=option2|name2=option1|name3=option1
...etc
All ExtraFields in the list need to have a value and I need all permutations in one format or another. It's a big list with a lot of permutations otherwise I'd do it by hand.
Well I did it... But I'm not proud of it. I'm sure there is a better way of doing it recursively. Hopefully this helps someone.
public List<String> GetFormPermutations(List<ExtraField> inList)
{
List<String> retList = new List<String>();
int[] listIndexes = new int[inList.Count];
for (int i = 0; i < listIndexes.Length; i++)
listIndexes[i] = 0;
while (listIndexes[inList.Count-1] < inList.ElementAt(inList.Count-1).Options.Count)
{
String cString = "";
//after this loop is complete. a line is done.
for (int i = 0; i < inList.Count; i++) {
String key = inList.ElementAt(i).Name;
Dictionary<String, String> cOptions = inList.ElementAt(i).Options;
String value = cOptions.ElementAt(listIndexes[i]).Value;
cString += key + "=" + value;
if (i < inList.Count - 1)
cString += "|";
}
retList.Add(cString);
listIndexes[0]++;
for(int i = 0; i < inList.Count -1; i++)
{
if (listIndexes[i] >= inList.ElementAt(i).Options.Count)
{
listIndexes[i] = 0;
listIndexes[i + 1]++;
}
}
}
return retList;
}
UPDATED ANSWER
So I managed to do it recursively. I haven't done this since college :D
Here's the whole class:
https://gist.github.com/Rastamas/8070ae7e1471d2183451a17bcf061376
PREVIOUS ANSWER BELOW
This goes through your list and adds the strings to a StringBuilder in the format you showed
foreach (var item in efList)
{
foreach (var option in item.Options)
{
stringBuilder.Append(String.Format("{0}={1}|", item.Name, option.Value));
}
stringBuilder.Remove(stringBuilder.Length - 1, 1);
stringBuilder.AppendLine();
}
Then you can just use stringBuilder.ToString() to get the whole list.
I'm trying to automate the nested foreach provided that there is a Master List holding List of strings as items for the following scenario.
Here for example I have 5 list of strings held by a master list lstMaster
List<string> lst1 = new List<string> { "1", "2" };
List<string> lst2 = new List<string> { "-" };
List<string> lst3 = new List<string> { "Jan", "Feb" };
List<string> lst4 = new List<string> { "-" };
List<string> lst5 = new List<string> { "2014", "2015" };
List<List<string>> lstMaster = new List<List<string>> { lst1, lst2, lst3, lst4, lst5 };
List<string> lstRes = new List<string>();
foreach (var item1 in lst1)
{
foreach (var item2 in lst2)
{
foreach (var item3 in lst3)
{
foreach (var item4 in lst4)
{
foreach (var item5 in lst5)
{
lstRes.Add(item1 + item2 + item3 + item4 + item5);
}
}
}
}
}
I want to automate the below for loop regardless of the number of list items held by the master list lstMaster
Just do a cross-join with each successive list:
IEnumerable<string> lstRes = new List<string> {null};
foreach(var list in lstMaster)
{
// cross join the current result with each member of the next list
lstRes = lstRes.SelectMany(o => list.Select(s => o + s));
}
results:
List<String> (8 items)
------------------------
1-Jan-2014
1-Jan-2015
1-Feb-2014
1-Feb-2015
2-Jan-2014
2-Jan-2015
2-Feb-2014
2-Feb-2015
Notes:
Declaring lstRes as an IEnumerable<string> prevents the unnecessary creation of additional lists that will be thrown away
with each iteration
The instinctual null is used so that the first cross-join will have something to build on (with strings, null + s = s)
To make this truly dynamic you need two arrays of int loop variables (index and count):
int numLoops = lstMaster.Count;
int[] loopIndex = new int[numLoops];
int[] loopCnt = new int[numLoops];
Then you need the logic to iterate through all these loopIndexes.
Init to start value (optional)
for(int i = 0; i < numLoops; i++) loopIndex[i] = 0;
for(int i = 0; i < numLoops; i++) loopCnt[i] = lstMaster[i].Count;
Finally a big loop that works through all combinations.
bool finished = false;
while(!finished)
{
// access current element
string line = "";
for(int i = 0; i < numLoops; i++)
{
line += lstMaster[i][loopIndex[i]];
}
llstRes.Add(line);
int n = numLoops-1;
for(;;)
{
// increment innermost loop
loopIndex[n]++;
// if at Cnt: reset, increment outer loop
if(loopIndex[n] < loopCnt[n]) break;
loopIndex[n] = 0;
n--;
if(n < 0)
{
finished=true;
break;
}
}
}
public static IEnumerable<IEnumerable<T>> GetPermutations<T>(this IEnumerable<IEnumerable<T>> lists)
{
IEnumerable<IEnumerable<T>> result = new List<IEnumerable<T>> { new List<T>() };
return lists.Aggregate(result, (current, list) => current.SelectMany(o => list.Select(s => o.Union(new[] { s }))));
}
var totalCombinations = 1;
foreach (var l in lstMaster)
{
totalCombinations *= l.Count == 0 ? 1 : l.Count;
}
var res = new string[totalCombinations];
for (int i = 0; i < lstMaster.Count; ++i)
{
var numOfEntries = totalCombinations / lstMaster[i].Count;
for (int j = 0; j < lstMaster[i].Count; ++j)
{
for (int k = numOfEntries * j; k < numOfEntries * (j + 1); ++k)
{
if (res[k] == null)
{
res[k] = lstMaster[i][j];
}
else
{
res[k] += lstMaster[i][j];
}
}
}
}
The algorithm starts from calculating how many combinations we need for all the sub lists.
When we know that we create a result array with exactly this number of entries. Then the algorithm iterates through all the sub lists, extract item from a sub list and calculates how many times the item should occur in the result and adds the item the specified number of times to the results. Moves to next item in the same list and adds to remaining fields (or as many as required if there is more than two items in the list). And it continues through all the sub lists and all the items.
One area though that needs improvement is when the list is empty. There is a risk of DivideByZeroException. I didn't add that. I'd prefer to focus on conveying the idea behind the calculations and didn't want to obfuscate it with additional checks.
I'm rather new to Linq. I'm having trouble coding this.
I have a list with many different sublists.
oldList[0] some type
oldList[1] another different type
oldList[2] the type I want
oldList[3] more types
I want to select all the parameters from a specific type and write them to a temp list.
If that temp list is empty, I want to assign some values (values don't actually matter).
After changing the values, I want to write temp list back into oldList.
Please advise. This is a huge learning experience for me.
public void myFunction(list)
{
//list contains at least 5 sublists of various type
//check if the type I want is null
IEnumerable<TypeIWant> possiblyEmptyList = list.OfType<TypeIWant>(); //find the type I want from the list and save it
if (possiblyEmptyList == null) //this doesn't work and possiblyEmptyList.Count <= 1 doesn't work
{
//convert residence address to forwarding address
IEnumerable<ReplacementType> replacementList = list.OfType<ReplacementType>();
forwardingAddress = replacementList.Select(x => new TypeIWant /* this statement functions exactly the way I want it to */
{
Address1 = x.Address1,
Address2 = x.Address2,
AddressType = x.AddressType,
City = x.City,
CountryId = x.CountryId,
CountyRegion = x.CountyRegion,
Email = x.Email,
ConfirmEmail = x.ConfirmEmail,
Fax = x.Fax,
Telephone = x.Telephone,
State = x.State,
PostalCode = x.PostalCode
});
//write forwarding address back to list
//don't know how to do this
}
LINQ purpose is querying. It doesn't allow you to replace some items in collection with other items. Use simple loop instead:
IEnumerable<TypeIWant> possiblyEmptyList = list.OfType<TypeIWant>();
if (!possiblyEmptyList.Any())
{
for (int i = 0; i < list.Count; i++)
{
ReplacementType item = list[i] as ReplacementType;
if (item == null)
continue;
list[i] = ConvertToTypeIWant(item);
}
}
And conversion (which is better to do with something like automapper):
private TypeIWant ConvertToTypeIWant(ReplacementType x)
{
return new TypeIWant
{
Address1 = x.Address1,
Address2 = x.Address2,
AddressType = x.AddressType,
City = x.City,
CountryId = x.CountryId,
CountyRegion = x.CountyRegion,
Email = x.Email,
ConfirmEmail = x.ConfirmEmail,
Fax = x.Fax,
Telephone = x.Telephone,
State = x.State,
PostalCode = x.PostalCode
};
}
Not LINQ but an example.
class Program
{
static void Main(string[] args)
{
// Vars
var list = new List<List<string>>();
var a = new List<string>();
var b = new List<string>();
var c = new List<string> { "one", "two", "three" };
var d = new List<string>();
// Add Lists
list.Add(a);
list.Add(b);
list.Add(c);
list.Add(d);
// Loop through list
foreach (var x in list)
{
if (x.Count < 1)
{
var tempList = new List<string>();
tempList.Add("some value");
x.Clear();
x.AddRange(tempList);
}
}
// Print
int count = 0;
foreach (var l in list)
{
count++;
Console.Write("(List " + count + ") ");
foreach (var s in l)
{
Console.Write(s + " ");
}
Console.WriteLine("");
}
}
}
(List 1) some value
(List 2) some value
(List 3) one two three
(List 4) some value