Concatenating two or more arrays in Javascript
I currently have a Javascript array of unknown length containing arrays of (unknown length) strings. I am looking for a way to find all possible combinations using one string from each second level array. Note: the order of the lines does not matter. That is, for:
[ [ 'a', 'b' ], [ 'c', 'd' ] ]
I would like to return:
[ 'ac', 'ad', 'bc', 'bd' ]
or if:
[
[
'a',
'b'
],
[
'1'
],
[
'i',
'j',
'k',
]
]
I would like to return:
[ 'a1i', 'a1j', 'a1k', 'b1i', 'b1j', 'b1k', ]
It seems to me that the answer lies in the recursive function, however I can't seem to get it to work (the variable scope gets confusing and it just falls flat).
Instead, I tried a different way of creating an array of results, looping through each subarray and placing each row in the results so that every possible combination was created:
function getArrayStrings(allTerms){
// get total number of possible combinations
var numberOfElements = 1;
$.each(allTerms, function(index, element){
numberOfElements *= element.length;
});
// create array of results
var result = [];
for(i = 0; i < numberOfElements; i ++){
result[i] = '';
}
// instantiate variables that will be used in loop
var elementToUse = 0;
var currentLength = 1;
var prevLength = 1;
// for each array, loop through values and add them to the relevant result element
$.each(allTerms, function(index, array){
// find length of current array
currentLength = array.length;
elementToUse = 0;
// for each of the elements in the results array
for(i = 0; i < numberOfElements; i ++){
// change the element to use if you've looped through the previous length (but not if it first result
if(i !== 0 && i % prevLength === 0){
elementToUse ++;
}
// return to using the first element if you've reached the last element in the sub array
if(elementToUse % currentLength === 0){
elementToUse = 0;
}
result[i] += '.' + array[elementToUse];
}
prevLength = array.length * prevLength;
});
console.log(result.join(''));
return result.join('');
}
This does work, however I wondered if anyone knew of a simpler function; I feel like this is what the Javascript (or jQuery) function already has, but I can't seem to find it.
Has anyone faced such a problem before? And if so, how did you approach him?
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Simple recursion:
var a = [ [ 'a', 'b' ],
[ '1' ],
[ 'i', 'j', 'k' ]
];
function combo( arr, i, j ) {
if (i===j-1) return arr[i];
var res = [];
arr[i].forEach( function(a) {
combo( arr, i+1, j ).forEach( function(b) {
res.push(a+b);
});
});
return res;
}
console.log( combo(a, 0, a.length) );
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I took advantage of the fact that you can combine auxiliary arrays in pairs. It seems a little more straightforward to me.
var input = [
['a','b'],
['1', '2','3','4'],
['i','j','k']
];
function getArrayStrings(input) {
function combine(arr1, arr2) {
var output = [];
for (var i=0;i<arr1.length;i++) {
for(var j=0;j<arr2.length;j++) {
output.push(arr1[i] + arr2[j]);
}
}
return output;
}
var output = [];
for(var i=0;i<input.length;i++) {
if (i==0) output = input[i];
else output = combine(output, input[i]);
}
return output;
}
var output = getArrayStrings(input);
console.log(output);
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It works.
var a = [['a','b'], ['1'],['i','j','k']],
b = [];
function cat(a1,a2){
var a = []
l = undefined;
while (a2.length > 0){
l = a2.shift();
a1.forEach(function(ele,idx,arr){
a.push(ele + l)
})
}
return a;
}
function merge(arr){
if (arr.length == 1){
return arr.shift()
} else {
var a1 = arr.shift()
return cat(a1,merge(arr))
}
}
var b = merge(a);
console.log(b)
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