PHP foreach previous element with string key

Question

I've this kind of array

Array
(
[12-12] => 9
[01-13] => 10
[02-13] => 11
[03-13] => 14
[05-13] => 16
[09-13] => 17
)

with a simple

 foreach ($arr as $key=>$value)

i can access every key and element.

But i need to get, from second element, also previous element:

$i=1;
foreach ($arr as $key=>$value) {
  if ($i==1) {
    echo $key .'=> 0 '.  $value;
  } else {
    echo $key .'=>'. $arr[$key-1] .'=>'. $value;
  }
 $i++
}

I need so to print a similar thing:

12-12 => 0 => 9
01-13 => 9 => 10
02-13 => 10 => 11

and so on

"Obviously" it doesn't function, because of string key. Any help? Thank you!

Why not store the current key in a variable outside the loop and change it at each iteration to the current key after you're done using it? — BOMEz
– BOMEz, Commented Sep 6, 2013 at 18:57

Ali · Accepted Answer · 2013-09-06 19:12:16Z

4

$previous_value = 0;
foreach ($arr as $key=>$value) {
    echo $key .'=>'. $previous_value .' '.  $value;
    $previous_value = $value;
}

This should solve it.

edited Sep 6, 2013 at 19:12

answered Sep 6, 2013 at 19:00

Ali

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1 Comment

sineverba Over a year ago

Perfect. Solved! Thank you very much to you and to others answering!

Chander · Accepted Answer · 2013-09-06 19:06:40Z

2

Many have talked about just storing the previous key, which I think is correct; but, for the sake of variety, you can also use array_keys, like so:

$keys=array_keys($arr);
$i=0;
foreach ($arr as $key=>$value) {
  if ($i==0) {
    echo $key .'=> 0 '.  $value;
  } else {
    echo $key .'=>'. $arr[$keys[$i-1]] .'=>'. $value;
  }
 $i++
}

See, $keys will contain an array with only the keys of $arr, so referring to $keys[$i] is the same as printing $key for record $i in a foreach loop. Sorry if I got it wrong, I think that's what you were trying to do, I hope.

Cheers.

answered Sep 6, 2013 at 19:06

Chander

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1 Comment

sineverba Over a year ago

i.e. this answer is more close to my "philosphy" than other answers. So, next time i'll try this, btw you did understand exactly what i need (I'm referring to your "Sorry if I got it wrong, I think that's what you were trying to do, I hope."

dognose · Accepted Answer · 2013-09-06 18:58:44Z

1

Just save the previous key.

    $prevKey = null;
    foreach ($arr as $key=>$value) {
      if ($i==1) {
        echo $key .'=> 0 '.  $value;
      } else {
        echo $key .'=>'. $arr[$prevKey] .'=>'. $value;
      }
    $prevKey = $key;

    }

answered Sep 6, 2013 at 18:58

dognose

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Comments

OneOfOne · Accepted Answer · 2013-09-06 18:59:08Z

1

You had the right idea, just wrong usage :

$prev = null;
foreach ($arr as $key=>$value) {
    if (is_array($prev)) {
        print_r($prev)
        echo $key .'=> 0 '.  $value;
    } else {
        echo $key .'=>'. $arr[$key-1] .'=>'. $value;
    }
    $prev = array($key, $value);
}

answered Sep 6, 2013 at 18:59

OneOfOne

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Comments

Mark Baker · Accepted Answer · 2013-09-06 18:59:14Z

1

Save the previous value in each iteration

$prevValue = 0;
foreach ($arr as $value) {
    echo $key . '=>' . $prevValue . '=>' . $value;
    $prevValue = $value;
}

answered Sep 6, 2013 at 18:59

Mark Baker

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1 Comment

sineverba Over a year ago

Perfect. Solved! Thank you very much to you and to others answering!

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