get previous array values in foreach

Question

My array :

$arr = array("jan","feb","mar","apr","mei","jun","jul","agu","sep","okt","nov","des");

then i do a foreach

foreach($arr as $ar){
  echo $ar;
}

that will output jan to des

my question is how do i display the previous values in current key?

For example, when I get to feb, I want to display jan too, when I get to jul, i want to display jun, etc.

score 56 · Accepted Answer · answered Nov 10 '10 at 20:00

56

$previousValue = null;
foreach($arr as $ar){
  echo $ar;
  if($previousValue) {
    echo $previousValue;
  }
  $previousValue = $ar;
}

answered Nov 10 '10 at 20:00

Matt Williamson

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1

This has the added advantage of working for arrays with string and non-sequential indices. – Aether Nov 10 '10 at 21:58

score 12 · Answer 2 · answered Nov 10 '10 at 20:00

12

You can use the keys to get the previous key.

foreach($arr as $key => $ar){
    $prev = $arr[$key-1];
    echo  "previous value -" .$prev;
}

You also have prev() as an internal array pointer:

$transport = array('foot', 'bike', 'car', 'plane');
$mode = current($transport); // $mode = 'foot';
$mode = next($transport);    // $mode = 'bike';
$mode = next($transport);    // $mode = 'car';
$mode = prev($transport);    // $mode = 'bike';
$mode = end($transport);     // $mode = 'plane';

answered Nov 10 '10 at 20:00

Elzo Valugi

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isn't this supposed to display current and previous? also won't this die on the first iteration? – dstarh Nov 10 '10 at 20:03
this is not happening inside a loop.. but it could happend. it is relative to the internal pointer of the current element – Elzo Valugi Nov 10 '10 at 20:05
6

This only works if your keys are integers and in order – W Biggs Feb 07 '19 at 18:36

score 2 · Answer 3 · answered Nov 10 '10 at 20:05

2

reset($array);
while($val=current($array))
{
    var_dump($val); // current
    var_dump(prev($array)); // previous
    next($array); // back to current
    next($array); // next
}

answered Nov 10 '10 at 20:05

bcosca

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score 1 · Answer 4 · edited Nov 23 '18 at 11:44

foreach ($arr as $key => $ar) {
    //check we aren't on jan (otherwise we get $key = -1 which doesn't work)
    if ($key != 0) {
        //print previous month followed by current month
        echo $arr[$key - 1] . '-' . $ar . '<br />';
    }
}

//OR, if you want to be able to roll through years then:

$last_key = end(array_keys($arr));
foreach ($arr as $key => $ar) {
    //check we aren't on jan
    if ($key != 0) {
        //print previous month followed by current month
        echo $arr[$key - 1] . ' - ' . $ar . '<br />';
    } else {
        echo $arr[$last_key] . ' - ' . $ar . '<br />';
    }
}

score 0 · Answer 5 · answered Nov 10 '10 at 20:01

0

for ( $i = 0; $i <count($arr); $i++) {
    echo $arr[$i]
    if($i > 0){
     echo $arr[$i-1]
   }
}

answered Nov 10 '10 at 20:01

dstarh

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score 0 · Answer 6 · edited May 23 '17 at 12:18

0

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

See this question and answer.

edited May 23 '17 at 12:18

Community

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1

answered Nov 10 '10 at 20:07

Thilo

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score 0 · Answer 7 · edited Nov 23 '18 at 11:22

A little more Dynamic

$arr  = array(
    "jan",
    "feb",
    "mar",
    "apr",
    "mei",
    "jun",
    "jul",
    "agu",
    "sep",
    "okt",
    "nov",
    "des"
);
$arr2 = $arr;
foreach ($arr as $k => $currVal) {
    unset($arr2[$k]);
    foreach ($arr2 as $k => $v) {
        $nextVal = $v;

        break;
    }
    echo "next val: " . $nextVal;
    echo "current val: " . $currVal;
}

get previous array values in foreach

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