Get the list of index for a string in an array?

Question

I have one array:

string[] cars = {"Volvo", "BMW", "Volvo", "Mazda","BMW","BMW"};

I m looking for the index of BMW, and I using below code to get:

Label1.Text = Array.FindIndex(filterlistinput, x => x.Contains("BMW")).ToString();

Unfortunately it return the result for the first BMW index only. Current output:

My expected output will be

{1,4,5}

Please refer this solution : [c# Array.FindAllIndexOf which FindAll IndexOf](https://stackoverflow.com/questions/10443461/c-sharp-array-findallindexof-which-findall-indexof) — Suyash Gaur, Jan 03 '20 at 08:20

Shahid Manzoor Bhat · Answer 1 · 2020-01-03T08:32:06.410

9

You can do something as follows

string[] cars = { "Volvo", "BMW", "Volvo", "Mazda", "BMW", "BMW" };
// Get indices of BMW 
var indicesArray = cars.Select((car, index) => car == "BMW" ? index : -1).Where(i => i != -1).ToArray();
// Display indices
Label1.Text = string.Join(", ", indicesArray);

edited Jan 03 '20 at 08:32

answered Jan 03 '20 at 08:22

Shahid Manzoor Bhat

1,307
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1

great solution :) – Pashupati Khanal Jan 03 '20 at 08:42

Furkan Öztürk · Accepted Answer · 2020-01-03T08:45:34.267

4

You can try the following,

string[] cars = {"Volvo", "BMW", "Volvo", "Mazda","BMW","BMW"};
//returns **{1,4,5}** as a list
var res = Enumerable.Range(0, cars.Length).Where(i => cars[i] == "BMW").ToList();
//joined items of list as 1,4,5
Label1.Text = string.Join(",", res);

edited Jan 03 '20 at 08:45

answered Jan 03 '20 at 08:28

Furkan Öztürk

1,178
11
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çok teşekkür ettim :) @snr – Furkan Öztürk Jan 03 '20 at 09:15
Enumerable.Range gayet akıllıca tebrikler. – Koray Elbek Jan 03 '20 at 09:19
teşekkür ederim @CoReeYe – Furkan Öztürk Jan 03 '20 at 09:20

score 3 · Answer 3 · answered Jan 03 '20 at 08:35

Previous answers are also ok. But I would do it like this if you need to do a lot of similar index searches. Will reduce the amount of code you write in the long term.

public static class SequenceExt
{
    public static IEnumerable<int> FindIndexes<T>(this IEnumerable<T> items, Func<T, bool> predicate)
    {
        int index = 0;
        foreach (T item in items)
        {
            if (predicate(item))
            {
                yield return index;
            }

            index++;
        }
    }
}

use it like this:

string[] cars = { "Volvo", "BMW", "Volvo", "Mazda", "BMW", "BMW" };
var indexes = cars.FindIndexes(s => s.Equals("BMW")).ToArray();

returns 1,4,5

Get the list of index for a string in an array?

3 Answers3