How to page an array using LINQ?

Question

If I have an array like this :

string[] mobile_numbers = plst.Where(r => !string.IsNullOrEmpty(r.Mobile))
                                          .Select(r => r.Mobile.ToString())
                                          .ToArray();

I want to paging this array and loop according to those pages .

Say the array count is 400 and i wanna to take the first 20 then the second 20 and so on until the end of array to process each 20 item .

How to do this with linq ? .

Have a look at http://stackoverflow.com/questions/419019/split-list-into-sublists-with-linq — Davio, Jun 13 '13 at 09:57

score 18 · Accepted Answer · edited Nov 13 '19 at 22:22

18

Use Skip and Take methods for paging (but keep in mind that it will iterate collection for each page you are going to take):

int pageSize = 20;
int pageNumber = 2;
var result = mobile_numbers.Skip(pageNumber * pageSize).Take(pageSize);

If you need just split array on 'pages' then consider to use MoreLinq (available from NuGet) Batch method:

var pages = mobile_numbers.Batch(pageSize);

If you don't want to use whole library, then take a look on Batch method implementation. Or use this extension method:

public static IEnumerable<IEnumerable<T>> Batch<T>(
     this IEnumerable<T> source, int size)
{
    T[] bucket = null;
    var count = 0;

    foreach (var item in source)
    {
        if (bucket == null)            
            bucket = new T[size];


        bucket[count++] = item;

        if (count != size)            
            continue;            

        yield return bucket;

        bucket = null;
        count = 0;
    }

    if (bucket != null && count > 0)
        yield return bucket.Take(count).ToArray();
}

Usage:

int pageSize = 20;
foreach(var page in mobile_numbers.Batch(pageSize))
{   
    foreach(var item in page)
       // use items
}

edited Nov 13 '19 at 22:22

Sergey Nudnov

1,217
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20

answered Jun 13 '13 at 09:56

Sergey Berezovskiy

224,436
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How to get the page number ?do i use this method in a loop right ? – Anyname Donotcare Jun 13 '13 at 09:58
@just_name you should provide page number for page you want. If you need to split you array on buckets, then consider to use MoreLinq Batch method – Sergey Berezovskiy Jun 13 '13 at 09:59
how to conclude the page number ,did u divide 400/20 to get the limit of loop ?? – Anyname Donotcare Jun 13 '13 at 10:00
`for(int i =0 i<20;i++) { }` – Anyname Donotcare Jun 13 '13 at 10:00
@just_name with batches you do `foreach(var page in pages)` – Sergey Berezovskiy Jun 13 '13 at 10:02
@MatthewWatson that's why I suggested to use batches – Sergey Berezovskiy Jun 13 '13 at 10:02
I use visual studio 2008 , i want it simple with a simple loop ,just i want the limit of loop to use – Anyname Donotcare Jun 13 '13 at 10:02
Added `ToArray()` there: `yield return bucket.Take(count).ToArray();` – Sergey Nudnov Nov 13 '19 at 20:13

score 2 · Answer 2 · answered Jun 13 '13 at 10:01

You need a batching operator.

There is one in MoreLinq that you can use.

You would use it like this (for your example):

foreach (var batch in mobile_numbers.Batch(20))
    process(batch);

batch in the above loop will be an IEnumerable of at most 20 items (the last batch may be smaller than 20; all the others will be 20 in length).

score 1 · Answer 3 · answered Jun 13 '13 at 09:56

1

You can use .Skip(n).Take(x); to skip to the current index and take the amount required.

Take will only take the number available, i.e. what's left, when the number available is less than requested.

answered Jun 13 '13 at 09:56

Grant Thomas

43,307
9
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How to page an array using LINQ?

3 Answers3