Convert string[] to int[] in one line of code using LINQ

Question

I have an array of integers in string form:

var arr = new string[] { "1", "2", "3", "4" };

I need to an array of 'real' integers to push it further:

void Foo(int[] arr) { .. }

I tried to cast int and it of course failed:

Foo(arr.Cast<int>.ToArray());

I can do next:

var list = new List<int>(arr.Length);
arr.ForEach(i => list.Add(Int32.Parse(i))); // maybe Convert.ToInt32() is better?
Foo(list.ToArray());

or

var list = new List<int>(arr.Length);
arr.ForEach(i =>
{
   int j;
   if (Int32.TryParse(i, out j)) // TryParse is faster, yeah
   {
      list.Add(j);
   }
 }
 Foo(list.ToArray());

but both looks ugly.

Is there any other ways to complete the task?

What's wrong with simply iterating through one collection, converting the value, and the adding it to the second? Seems pretty clear in intention to me. — Ed Swangren
– Ed Swangren, Commented Aug 19, 2009 at 0:11
Just FYI, I'm using this question here: stackoverflow.com/questions/1297325/… — Allen Rice
– Allen Rice, Commented Aug 19, 2009 at 0:49
TryParse is not faster (except if your strings are invalid, but in that case you want the exception to alert you). — usr
– usr, Commented Jun 9, 2012 at 18:34

Ahmad Mageed · Accepted Answer · 2012-06-09 18:25:08Z

719

Given an array you can use the Array.ConvertAll method:

int[] myInts = Array.ConvertAll(arr, s => int.Parse(s));

Thanks to Marc Gravell for pointing out that the lambda can be omitted, yielding a shorter version shown below:

int[] myInts = Array.ConvertAll(arr, int.Parse);

A LINQ solution is similar, except you would need the extra ToArray call to get an array:

int[] myInts = arr.Select(int.Parse).ToArray();

edited Jun 9, 2012 at 18:25

answered Aug 19, 2009 at 0:15

Ahmad Mageed

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8 Comments

spender Over a year ago

Nice. Didn't know that one. +1

Marc Gravell Over a year ago

Actually, you don't need the lambda; ConvertAll(arr, int.Parse) is sufficient

BSalita Over a year ago

Lambda is needed in VB.Net 2010: uArray = Array.ConvertAll(sNums.Split(","), Function(i) UInteger.Parse(i))

Slai Over a year ago

@BSalita No, in VB.Net it's Array.ConvertAll(arr, AddressOf Integer.Parse)

Ahmad Mageed Over a year ago

@AmrAlaa congrats, you're the first downvoter :) Seriously though, the original question shows an approach using TryParse, so if anyone wants to check for errors that's one option, with some drawbacks. I don't disagree with you; error checking is important, but I feel the answer was sufficient for the question and did not get exhaustive about error checking. StackOverflow should point you to a solution, but that doesn't mean it should be copy-pasted into our projects without reflection and enhancements as needed.

|

Simon Fox · Accepted Answer · 2009-08-19 00:17:13Z

37

EDIT: to convert to array

int[] asIntegers = arr.Select(s => int.Parse(s)).ToArray();

This should do the trick:

var asIntegers = arr.Select(s => int.Parse(s));

edited Aug 19, 2009 at 0:17

answered Aug 19, 2009 at 0:11

Simon Fox

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2 Comments

spender Over a year ago

.ToArray() required to satisfy OP's question

Simon Fox Over a year ago

change var to int[] and append .ToArray() if you need it as an int array

Slai · Accepted Answer · 2018-08-06 15:09:53Z

30

To avoid exceptions with .Parse, here are some .TryParse alternatives.

To use only the elements that can be parsed:

string[] arr = { null, " ", " 1 ", " 002 ", "3.0" };
int i = 0; 
var a = (from s in arr where int.TryParse(s, out i) select i).ToArray();  // a = { 1, 2 }

or

var a = arr.SelectMany(s => int.TryParse(s, out i) ? new[] { i } : new int[0]).ToArray();

Alternatives using 0 for the elements that can't be parsed:

int i; 
var a = Array.ConvertAll(arr, s => int.TryParse(s, out i) ? i : 0); //a = { 0, 0, 1, 2, 0 }

or

var a = arr.Select((s, i) => int.TryParse(s, out i) ? i : 0).ToArray();

C# 7.0:

var a = Array.ConvertAll(arr, s => int.TryParse(s, out var i) ? i : 0);

edited Aug 6, 2018 at 15:09

answered May 4, 2016 at 16:21

Slai

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7 Comments

Beetee Over a year ago

The second solution: var a = Enumerable.Range(0, arr.Length).Where(i => int.TryParse(arr[i], out i)).ToArray(); just returns the indeces 0,1,2,... instead of the real values. What's the right solution here?

Slai Over a year ago

Thanks @Beetee. Not sure what I was thinking with that. I replaced it with another alternative.

Beetee Over a year ago

@Slai: Thanks. But what does new int[0]? When I have text, I don't get a 0 in my array...

Slai Over a year ago

@Beetee new int[0] is an empty int array. The first two examples skip values that can't be parsed, and the last two examples use 0 for values that can't be parsed.

Beetee Over a year ago

@Slai: Ah now I get it. I mixed it up with new int[] {0}. Thx.

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A.Dara · Accepted Answer · 2012-06-09 13:07:01Z

14

you can simply cast a string array to int array by:

var converted = arr.Select(int.Parse)

answered Jun 9, 2012 at 13:07

A.Dara

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1 Comment

Mafu Josh Over a year ago

nice! thankyou. And in VB.Net Dim converted = arr.Select(addressof Integer.Parse)

abatishchev · Accepted Answer · 2009-08-19 00:16:27Z

4

var asIntegers = arr.Select(s => int.Parse(s)).ToArray();

Have to make sure you are not getting an IEnumerable<int> as a return

edited Aug 19, 2009 at 0:16

abatishchev

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answered Aug 19, 2009 at 0:15

Rob

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Comments

sepp2k · Accepted Answer · 2009-08-19 00:12:40Z

3

var list = arr.Select(i => Int32.Parse(i));

answered Aug 19, 2009 at 0:12

sepp2k

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