Create new list from a old list using a lambda function

Question

I have the following: List<InputRow> which contains a number of InputRow objects.

I am wondering if there is a way for me to use a lambda function on my original list to give me a new List where InputRow.someProperty > 1 for all the objects.

This would leave me with a list of InputRow objects all having someProperty greater than 1.

possible duplicate of [using LINQ to remove objects within a List](http://stackoverflow.com/questions/853526/using-linq-to-remove-objects-within-a-listt) — Muad'Dib, Apr 23 '12 at 19:18

score 7 · Answer 1 · answered Apr 23 '12 at 19:15

7

You can of course also do this:

var list = new List<string>(){ "a", "b", "c" };

list.RemoveAll(s => s == "b");

which removes the items in place instead of creating a new list.

answered Apr 23 '12 at 19:15

Phil

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score 6 · Accepted Answer · answered Apr 23 '12 at 19:13

6

You could use LINQ (a conjunction of the .Where() and .ToList() extension methods):

List<InputRow> originalList = ...
List<InputRow> filteredList = originalList
    .Where(x => x.someProperty > 1)
    .ToList();

answered Apr 23 '12 at 19:13

Darin Dimitrov

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Using `RemoveAll` on the List avoids deleting and re-creating the list. – Servy Apr 23 '12 at 19:18
@Servy Baxter wants those results not remove them – Nikhil Agrawal Apr 23 '12 at 19:19
@Servy Can you elaborate on the usage of RemoveAll? I could flip the statement to say RemoveAll less than or equal to 1. I am just not sure what the syntax for that would be. – Baxter Apr 23 '12 at 19:23
list.RemoveAll(x => x.SomeProperty<=1); – Nikhil Agrawal Apr 23 '12 at 19:24
@NikhilAgrawal You can either logically refactor the lambda to mean the opposite (simple enough in this case), or you can just add a NOT outside of the whole thing to cover the general case. – Servy Apr 23 '12 at 19:25
To turn true into false just add ! list.RemoveAll(x => !(x.SomeProperty<=1)); – Nikhil Agrawal Apr 23 '12 at 19:26
Excellent, thank you for all the great answers / comments on this. I have a much better idea of how to use those now. – Baxter Apr 23 '12 at 19:28

score 3 · Answer 3 · answered Apr 23 '12 at 19:13

3

Sure. You can do this:

var newList = inputRowList.Where(inputRow => inputRow.someProperty > 1).ToList();

answered Apr 23 '12 at 19:13

Smur

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score 2 · Answer 4 · answered Apr 23 '12 at 19:13

2

List<InputRow> newlist = oldlist.Where(x => x.someProperty > 1).ToList();

This will search your old list on the condition that someProperty > 1 and convert the result into List using .ToList()

answered Apr 23 '12 at 19:13

Nikhil Agrawal

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Create new list from a old list using a lambda function

4 Answers4