CODEWITHSUNDEEP
c#arraysstringreplace
Praveen Prasannan
Praveen Prasannan

Reputation: 7123

Replace all occurences of a string from a string array

I have a string array like:

 string [] items = {"one","two","three","one","two","one"};

I would like to replace all ones with zero at once. Then items should be:

{"zero","two","three","zero","two","zero"};

I found one solution How do I replace an item in a string array?.

But it will replace the first occurrence only. Which is the best method/approach to replace all occurrences?

Upvotes: 10

Views: 81938

Answers (8)

Praveen Prasannan
Praveen Prasannan

Reputation: 7123

string [] items = {"one","two","three","one","two","one"};
items =  items.Select(s => s!= "one" ? s : "zero").ToArray();

Found answer from here.

Upvotes: 3

Jeppe Stig Nielsen
Jeppe Stig Nielsen

Reputation: 61952

You can also do it in parallel:

Parallel.For(0, items.Length,
  idx => { if(items[idx] == "one") { item[idx] = "zero"; } });

Upvotes: 3

phoog
phoog

Reputation: 43046

Sorry, you have to loop. There's no getting around it.

Also, all of the other answers give you a new array with the desired elements. If you want the same array to have its elements modified, as your question implies, you should just do it like this.

for (int index = 0; index < items.Length; index++)
    if (items[index] == "one")
        items[index] = "zero";

Simple.

To avoid writing a loop in your code every time you need this to happen, create a method:

void ReplaceAll(string[] items, string oldValue, string newValue)
{
    for (int index = 0; index < items.Length; index++)
        if (items[index] == oldValue)
            items[index] = newValue;
}

Then call it like this:

ReplaceAll(items, "one", "zero");

You can also make it into an extension method:

static class ArrayExtensions
{
    public static void ReplaceAll(this string[] items, string oldValue, string newValue)
    {
        for (int index = 0; index < items.Length; index++)
            if (items[index] == oldValue)
                items[index] = newValue;
    }
}

Then you can call it like this:

items.ReplaceAll("one", "zero");

While you're at it, you might want to make it generic:

static class ArrayExtensions
{
    public static void ReplaceAll<T>(this T[] items, T oldValue, T newValue)
    {
        for (int index = 0; index < items.Length; index++)
            if (items[index].Equals(oldValue))
                items[index] = newValue;
    }
}

The call site looks the same.

Now, none of these approaches supports custom string equality checking. For example, you might want the comparison to be case sensitive, or not. Add an overload that takes an IEqualityComparer<T>, so you can supply the comparison you like; this is much more flexible, whether T is string or something else:

static class ArrayExtensions
{
    public static void ReplaceAll<T>(this T[] items, T oldValue, T newValue)
    {
        items.ReplaceAll(oldValue, newValue, EqualityComparer<T>.Default);
    }

    public static void ReplaceAll<T>(this T[] items, T oldValue, T newValue, IEqualityComparer<T> comparer)
    {
        for (int index = 0; index < items.Length; index++)
            if (comparer.Equals(items[index], oldValue))
                items[index] = newValue;
    }
}

Upvotes: 10

Anirudha
Anirudha

Reputation: 32807

string[] items = { "one", "two", "three", "one", "two", "one" };

If you want it the index way as you specified:

int n=0;
while (true)
{
n = Array.IndexOf(items, "one", n);
if (n == -1) break;
items[n] = "zero";
}

But LINQ would be better

var lst = from item in items
select item == "one" ? "zero" : item;

Upvotes: 1

Daniel MesSer
Daniel MesSer

Reputation: 1181

There is one way to replace it without looping through each element:

 string [] items = {"zero","two","three","zero","two","zero"};

Other than that, you have to iterate through the array (for/lambda/foreach)

Upvotes: 14

benjamin54
benjamin54

Reputation: 1300

string[] newarry = items.Select(str => { if (str.Equals("one")) str = "zero"; return str; }).ToArray();

Upvotes: 0

Yograj Gupta
Yograj Gupta

Reputation: 9869

You can try this, but I think, It will do looping also.

string [] items = {"one","two","three","one","two","one"};
var str= string.Join(",", items);
var newArray = str.Replace("one","zero").Split(new char[]{','});

Upvotes: 2

Simon Whitehead
Simon Whitehead

Reputation: 65077

Theres no way to do that without looping.. even something like this loops internally:

string [] items = {"one","two","three","one","two","one"};

string[] items2 = items.Select(x => x.Replace("one", "zero")).ToArray();

I'm not sure why your requirement is that you can't loop.. however, it will always need to loop.

Upvotes: 40

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