Combine multiple array to another array

Question

i want combine 2 array like this

Example 1 :

Arr1 = ['A','B','C'],
Arr2 = ['D','E']

will be become

Arr3 = [
  ['A','D'],['A','E'],['B','D'],['B','E'],['',''] ....
]

Example 2 :

Arr1 = ['A','B','C'],
Arr2 = ['D','E']
Arr3 = ['G','H']

will be become

Arr4 = [
  ['A','D','G'],['A','E','G'],['','',''].... 
]

Any idea or suggest me algorithm can be like this thanks so much

Two foreach loops. Your second example (also named Ex1) is not detailed enough for us to know what is happening. — Andreas, Sep 20 '17 at 03:08
Sounds like you're looking for the cartesian product of two arrays. Perhaps [this answer](https://stackoverflow.com/a/6313346/4548148) could help? — tugayac, Sep 20 '17 at 03:11
This my answer https://stackoverflow.com/questions/6311779/finding-cartesian-product-with-php-associative-arrays thanks so much my friend @tugayac — Vui Dang, Sep 20 '17 at 03:24

score 1 · Answer 1 · answered Sep 20 '17 at 05:04

Simplified version; merging array by index

$arr1 = range('a', 'b');
$arr2 = range('c', 'f');
$arr3 = range('g', 'k');
$arr4 = range('x', 'z');
$res  = array();

// $counter = 1;
// while ($counter <= 4) {
//   $array = "arr{$counter}";
//   funcIndexMerge($res, $$array);
//   $counter++;
// }

funcIndexMerge($res, $arr1);
funcIndexMerge($res, $arr2);
funcIndexMerge($res, $arr3);
funcIndexMerge($res, $arr4);
var_export($res);

function funcIndexMerge(&$res, $array) {
    foreach ($array as $ari => $val)  {
        if (!isset($res[$ari])) {
            $res[$ari] = array();
        }
        $res[$ari] = array_merge($res[$ari], array($val));
    }
 }

score 1 · Answer 2 · answered Sep 20 '17 at 05:48

The problem you suggest is very similar to this Leetcode Challenge. The idea is to use Backtracking

Psuedo PsedoCode :

result := string Array
CartesianProduct(rowIndex, ArrayList, stringSoFar):

if rowIndex equal ArrayList.size:
    Add stringSoFar to result
    return
for(eachItem in ArrayList[rowIndex])
    CartesianProduct(rowIndex +1 , ArrayList, stringSoFar + eachItem)
    return

This is a workhorse which does all the computation and can be called like CartesianProduct(0, list of Array to be multiplied, "")

Suppose your ArrayList = [['A'], ['C', 'D']]. And CP be CartesianProduct

                 CP(0, AL, "")
            (Take 'A')/
                     /
               CP(1, AL, "A") (stringSoFar becomes 'A')
         (Take C) /       \(Take 'D'.Second Iteration with second array['C', 'D']) 
                 /         \
         CP(2, AL, "AC")  CP(2, AL, "AD")
              /              \
  rowIndex equal size.   rowIndex equals listSize i.e No more list to look
  Add "AC" and return    Add stringsoFar ("AD") to result and rerturn

My solution to the Leetcode problem(but in C++). Hopefully it'll give you some idea to write in PHP

class Solution {
public:
    map<char, vector<string>> values {
    {'2', vector<string>{"a", "b", "c"}},
    {'3', vector<string>{"d", "e", "f"}},
    {'4', vector<string>{"g", "h", "i"}},
    {'5', vector<string>{"j", "k", "l"}},
    {'6', vector<string>{"m", "n", "o"}},
    {'7', vector<string>{"p", "q", "r", "s"}},
    {'8', vector<string>{"t", "u", "v"}},
    {'9', vector<string>{"w", "x", "y", "z"}}
    };
vector<string> answer;
void doComb(int index, string digits, string sofar)
{
    if(index == digits.size())
    {
        if(sofar != "")
        {
            answer.push_back(sofar);    
        }
        return;
    }
    for(auto lett : values[digits[index]])
    {
        doComb(index + 1, digits, sofar + lett);
    }
    return;
}
vector<string> letterCombinations(string digits) {
    doComb(0, digits, "");
    return answer;
    }
};

Combine multiple array to another array

2 Answers2

Linked