Functional Helpers

Filter Values

array_filter keeps only the values accepted by a callback.

keep matching values Filtering is useful when the callback can answer yes or no for each value.

Filter Values

extra
filter_values.php
Replay: real traced execution (multi-file project)
<?php
function is_even($value) {
    return $value % 2 === 0;
}

$extra = 5;
$values = [2, $extra, 6];
$kept = array_filter($values, "is_even");
$summary = implode(",", $kept);
$count = count($kept);

echo "extra=" . $extra . "\n";
echo "count=" . $count . "\n";
echo "kept=" . $summary . "\n";

<?php
function is_even($value) {
    return $value % 2 === 0;
}

$extra = 1;
$values = [2, $extra, 6];
$kept = array_filter($values, "is_even");
$summary = implode(",", $kept);
$count = count($kept);

echo "extra=" . $extra . "\n";
echo "count=" . $count . "\n";
echo "kept=" . $summary . "\n";

<?php
function is_even($value) {
    return $value % 2 === 0;
}

$extra = 8;
$values = [2, $extra, 6];
$kept = array_filter($values, "is_even");
$summary = implode(",", $kept);
$count = count($kept);

echo "extra=" . $extra . "\n";
echo "count=" . $count . "\n";
echo "kept=" . $summary . "\n";

  1. $extra ← 5, $values ← Array

    6$extra→ 5 = 5; //@extra=1, 87$values→ Array = [2, $extra5, 6];8$kept = array_filter($valuesArray, "is_even");9$summary = implode(",", $kept);

  2. function is_even($value)

    pass 1 of 3
    1<?php2function is_even($value2) {3    return $value2 % 2 === 0;4}
    All 3 passes — pass 1 is the card above
    pass$value
    12
    25
    36

  3. $kept ← Array, $summary ← 2,6, $count ← 2

    7$values = [2, $extra, 6];8$kept→ Array = array_filter($valuesArray, "is_even");9$summary→ 2,6 = implode(",", $keptArray);10$count→ 2 = count($keptArray);1112echo "extra=" . $extra5 . "\n";13echo "count=" . $count2 . "\n";14echo "kept=" . $summary2,6 . "\n";
    outputextra=5
count=2
kept=2,6

  1. $extra ← 1, $values ← Array

    6$extra→ 1 = 1;7$values→ Array = [2, $extra1, 6];8$kept = array_filter($valuesArray, "is_even");9$summary = implode(",", $kept);

  2. function is_even($value)

    pass 1 of 3
    1<?php2function is_even($value2) {3    return $value2 % 2 === 0;4}
    All 3 passes — pass 1 is the card above
    pass$value
    12
    21
    36

  3. $kept ← Array, $summary ← 2,6, $count ← 2

    7$values = [2, $extra, 6];8$kept→ Array = array_filter($valuesArray, "is_even");9$summary→ 2,6 = implode(",", $keptArray);10$count→ 2 = count($keptArray);1112echo "extra=" . $extra1 . "\n";13echo "count=" . $count2 . "\n";14echo "kept=" . $summary2,6 . "\n";
    outputextra=1
count=2
kept=2,6

  1. $extra ← 8, $values ← Array

    6$extra→ 8 = 8;7$values→ Array = [2, $extra8, 6];8$kept = array_filter($valuesArray, "is_even");9$summary = implode(",", $kept);

  2. function is_even($value)

    pass 1 of 3
    1<?php2function is_even($value2) {3    return $value2 % 2 === 0;4}
    All 3 passes — pass 1 is the card above
    pass$value
    12
    28
    36

  3. $kept ← Array, $summary ← 2,8,6, $count ← 3

    7$values = [2, $extra, 6];8$kept→ Array = array_filter($valuesArray, "is_even");9$summary→ 2,8,6 = implode(",", $keptArray);10$count→ 3 = count($keptArray);1112echo "extra=" . $extra8 . "\n";13echo "count=" . $count3 . "\n";14echo "kept=" . $summary2,8,6 . "\n";
    outputextra=8
count=3
kept=2,8,6