A new array out of some values from existing array

Question

If I got an array like:

string[] test = new string[5] { "hello", "world", "test", "world", "world"};

How can I make a new array out of the ones that is the same string, "world" that is where you on before hand know how many there are, here 3?

I was thinking of something like:

string[] newArray = new string[3];

        for (int i = 0; i < 5; i++)
        {
            if (test[i].Contains("world"))
            {
                newArray[i] = test[i];
            }
        }

The problem is here: newArray[i] = test[i];

Since it's iterating from 0 to 4, there's gonna be an error since newArray is limited to 3.

How do solve this?

EDIT: I need it to be that from test (the old array) position 1, 3 and 4 should be stored at 0, 1 and 2 in the newArray.

Could you write the output you want exactly as you did for the input? It would help us (at least me) to understand exactly what you want. — Cédric Bignon
– Cédric Bignon, Commented Jul 25, 2013 at 22:56
@CédricBignon I would like the output to be something like "newArray contains the following strings: world, world, world". Is that how you meant? — Erik
– Erik, Commented Jul 25, 2013 at 22:58
@Erik It was more like string[] output = new string[3] { "world", "world", "world"}. What do you want as output for the following input { "hello", "world", "hello", "hello", "test", "my world", "world"}? — Cédric Bignon
– Cédric Bignon, Commented Jul 25, 2013 at 23:00
@Erik: that's exactly what the 2 answers with 0 upvotes tried to do from the start. Not sure if that's what you actually want though. — Ma3x
– Ma3x, Commented Jul 25, 2013 at 23:08
Then I'd want string[] output = new string[3] { "world", "world", "world"} since it's still 3 strings that contains "world". Thanks. — Erik
– Erik, Commented Jul 25, 2013 at 23:08

Alden · Accepted Answer · 2013-07-25 22:57:39Z

5

You want to use Linq:

var newArray = test.Where(x => x.Contains("world")).ToArray();

answered Jul 25, 2013 at 22:57

Alden

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Comments

Simon Whitehead · Accepted Answer · 2013-07-25 22:57:20Z

4

Use a List<string> instead:

    List<string> newList = new List<string>();

    for (int i = 0; i < 5; i++)
    {
        if (test[i].Contains("world"))
        {
            newList.Add(test[i]);
        }
    }

If you really need it as an array later.. convert the list:

string[] newArray = newList.ToArray();

answered Jul 25, 2013 at 22:57

Simon Whitehead

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Comments

PurkkaKoodari · Accepted Answer · 2013-07-25 22:58:58Z

1

You are using the same index i for both test and newArray. I would suggest you create another counter variable and increment it:

string[] newArray = new string[3];
int counter = 0;

for (int i = 0; i < 5; i++)
{
    if (test[i].Contains("world"))
    {
        newArray[counter] = test[i];
        counter++;
    }
}

answered Jul 25, 2013 at 22:58

PurkkaKoodari

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3 Comments

Sayse Over a year ago

@Erik - this will work, I would also extend this further and break out of the for loop if counter is >= newArray.Length

Erik Over a year ago

I'm sorry again. I misread, it's late here, hehe. Your logic is correct, I'll see if I can apply this logic.

Erik Over a year ago

Accepted this as it was the simplest applicable and working solution in my case, even though most answers will work just as great (and some even better).

Sayse · Accepted Answer · 2013-07-25 23:12:59Z

1

This isn't technically your question but if you wish to make a load of arrays based of those with the same word you could do

test.GroupBy(x => x).ToList();

this will give you a List of Lists.. with your test data this will be

list1 - hello
list2 - world world world
list3 - test

Example use

var lists =  test.GroupBy(x => x).ToList();
foreach(var list in lists)
{
     foreach(var str in list)
     {
         Console.WriteLine(str);
     } 
     Console.WriteLine();
}

edited Jul 25, 2013 at 23:12

answered Jul 25, 2013 at 23:04

Sayse

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Comments

Ma3x · Accepted Answer · 2013-07-25 23:13:21Z

1

With an extra helper index variable

    string[] newArray = new string[3];

    for (int i = 0, j = 0; i < 5; i++)
    {
        if (test[i].Contains("world"))
        {
            newArray[j++] = test[i];
            if (j >= newArray.Length)
                break;
        }
    }

edited Jul 25, 2013 at 23:13

answered Jul 25, 2013 at 22:58

Ma3x

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9 Comments

Alden Over a year ago

this won't work if there are more than 3 strings with "world". edit: didn't see that the question said you already know there are 3

Ma3x Over a year ago

@Alden: well that was his requirement, not mine. He defined array at 3. Read his question conditions, I am just answering.

Sayse Over a year ago

or more than 5 elements in the array, and OP says if his array was like that, meaning thats not his actual data

PurkkaKoodari Over a year ago

@Alden The question said, "where you on before hand know how many there are, here 3".

Sayse Over a year ago

Personally I think its awful coding including two for loops in the same line as you have. I also still don't think your code would work if there were suddenly 4 "worlds", OP would have to update this code which is just tedious and error prone

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