How to use portion of an array in loop?

Question

I have an array:

$array = array();
$array[0] = "string";
$array[1] = "string1";
$array[2] = "string2";
$array[3] = "string3";
...
$array[99] = "string99";
$array[100] = "string100";

If I want to work with all the values of the array:

foreach ($array as $key => $value)
{
    // Do something with the value
}

Depending on a condition, I might need to work with only portion of the array (for example 50-100). How do I extract key 50-100 from the array?

There is this way but it doesn't seem much efficient:

foreach ($array as $key => $value)
{
    if ($key > 49)
    {
        // Do something with the value
    }
}

Are there any better, more-efficient ways to do it?

The answers from patryk-uszynski, NN, and arkascha will all work, but I thing patryk-uszynski's is best for this example! — Ben Hillier, Jan 12 '17 at 12:13

Patryk Uszyński · Accepted Answer · 2017-01-24T11:14:20.767

3

Array in your question has numerical indexes, so you can use for loop. Then only keys in specified range will be processed. When you are using foreach all elements will be.

Example for range <50,100>

for($i=50; $i<=100; $i++) {
    //do something with $array[$i]
}

All others key wont be processed. You can also use functions like array_slice(), but it wont be such efficient.

edited Jan 24 '17 at 11:14

answered Jan 12 '17 at 12:10

Patryk Uszyński

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score 2 · Answer 2 · answered Jan 12 '17 at 12:09

PHP offers the function array_slice() for that:

An example using only the elements from key 50 upwards:

foreach (array_slice($array, 50) as $key => $value) {
    // Do something with the value
}

Using only 10 entries with an offset of 50, to elements 50-60:

foreach (array_slice($array, 50, 10) as $key => $value) {
    // Do something with the value
}

That function allows you to specify a length and an optional offset for the resulting part of the array.

See the documentation: http://php.net/manual/en/function.array-slice.php

score 0 · Answer 3 · answered Jan 12 '17 at 12:09

0

use array slice

 array_slice($array, 50, 100);

answered Jan 12 '17 at 12:09

Nishant Nair

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Welcome @TrondroMulligan – Nishant Nair Jan 12 '17 at 12:12

Yasar Arafath · Answer 4 · 2017-01-12T12:14:16.667

0

foreach ($array as $key => $value)
{
    if ($key < 50 OR $key > 101)
    {
        continue;
    }
}

edited Jan 12 '17 at 12:14

answered Jan 12 '17 at 12:10

Yasar Arafath

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Won't I still be looping through the 100 keys? – Trondro Mulligan Jan 12 '17 at 12:11
Yes because `foreach` as is said, always will be iterating throught all elements of array. – Patryk Uszyński Jan 12 '17 at 12:15
If you want to loop only those values then you should use like this array_slice($array, 50, 100); – Yasar Arafath Jan 12 '17 at 12:17
1

@YasarArafath be very careful with using `OR`. It might not behave the way you think it does. Please read http://stackoverflow.com/questions/2803321/and-vs-as-operator for details. While in your answer it will work. If you're assigning values it could go really messy. – dokgu Jan 12 '17 at 16:33

How to use portion of an array in loop?

4 Answers4