3

I have values 1,2,3 and it will create another value like below and produce results by summing. As there are 3 values so that it will create three arrays. if it were 5 values then 5 such arrays are required.

1 2 3
  1 2 3
    1 2 3

Result is : 1 3 6 5 3

What I am doing is :

$a=[1,2,3];

$b=$a;
$c=$a;
$d=[];
    
array_push($a,0,0);
array_unshift($b,0);
array_push($b,0);
array_unshift($c,0,0);

$d = array_map(function () {
    return array_sum(func_get_args());
}, $a,$b,$c);

print_r($d);

I am not able to find the way to do this for more values than 3 and dynamically. So that I have to just put the values and it gives me the result. I am not asking for the code but you can help me with that how I should approach it. Thanks.

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1
  • If x is the length of the number, The length of Resultant figure will be having (x *2) -1 items , so you may put zero to the end/ start of each set and sum them up to get the final data items Commented Jul 28, 2021 at 9:32

3 Answers 3

Reset to default
4

I recommend a linear approach with no preparations or padding or data bloat.

Use the indexes and simple arithmetic to add values to their desired element in the output.

Code: (Demo)

$array = range(1, 3);
$result = [];
foreach ($array as $shifter => $unused) {
    foreach ($array as $index => $value) {
        $key = $shifter + $index;
        $result[$key] = ($result[$key] ?? 0) + $value;
    }
}
var_export($result);
// [1, 3, 6, 5, 3]

This is very clean, readable, maintainable, and most efficient.

While $shifter = 0, $key will be 0, 1 then 2; forming [1, 2, 3].
While $shifter = 1, $key will be 1, 2 then 3; forming [1, 3, 5, 3].
While $shifter = 2, $key will be 2, 3 then 4; forming [1, 3, 6, 5, 3].

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2 Comments

Simple is beautiful
Thats nice, I like it!
3

If you're using PHP 7.4+ you can use the below...

// Ensure the keys are indexed not associative.
$input = array_values( [ 1, 2, 3, 4, 5 ] );

// Create rows.
$rows = [];
foreach ( $input as $key => $value ) {
    $rows[ $key ] = array_merge( array_fill( 0, $key, 0 ), $input );
}

// Sum values.
$output = array_map( function() {
    return array_sum( func_get_args() );
}, ...$rows );

If you're using a PHP version below 7.4 you can do...

// Ensure the keys are indexed not associative.
$input = array_values( [ 1, 2, 3 ] );

// Create rows.
$rows = [];
foreach ( $input as $key => $value ) {
    $rows[ $key ] = array_merge( array_fill( 0, $key, 0 ), $input );
}

// Sum values.
$output = call_user_func_array( 'array_map', array_merge( [ function() {
    return array_sum( func_get_args() );
} ], $rows ) );
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1 Comment

This is solution is fine for small data sets. For larger arrays, I would recommend using @mickmackusa answer much more performant.
0

I'm thinking using an offset makes sense, it's the same as your approach, except I'm adding a 0 using array_fill

$arr = [1,2,3];
$result = [];
$offset = 0;
for($i = 0; $i < count($arr); $i++) {

    $result = array_map(function () {
        return array_sum(func_get_args());
    }, $result, array_merge(array_fill(0, $offset, 0), $arr));

    $offset++;
}

var_dump($result);

The advantage of using this is that it uses very little memory even for a very large initial array.

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3 Comments

Shouldn't $i < 3 be replaced with $i < count($arr)? Otherwise you're limited to 3 items in the array.
I understood the question as him wanting to be able to change the number on demand, which means that the 3 can become a 300 if he so wishes, I didn't think that he meant it to match the number of elements in the original array, neither am I sure if he wants the arrays to be the same. But re-reading the question does show that he does, meaning I'll just use the count, thanks for the tip.
The question states that OP wants to "duplicate array"

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