javascript - Dynamic nested for loops to be solved with recursion - Stack Overflow

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I'm trying to get a result looking something like this: Miniors | Boys | 54kg - 62kg where every value delimited by a pipe | es from an array containing a certain "type of restriction". For example: ageGroups, genders, weightClasses (as seen above).

The way I'm able to get this result right now is if I hard code the nested forEach-loops (using underscorejs), but this means I have to now how many arrays I have to loop over to get wanted result. This works "fine":

var categories = [];
_.each(ageGroups, function(ageGroup) {
   _.each(gender, function(gender) {
     _.each(weightClasses, function(weightClass) {
       categories.push(ageGroup.name + ' | ' + gender.name + ' | ' + weightClass.name);
      });
   });
});

The output is an array (categories) with all the possible binations of the restriction arrays.

Now, my problem is that I need a way to do the same with an unknown number of restriction arrays. My guess for a proper solution is recursion, BUT I haven't been able to produce anything that actually works since I'm not able to wrap my head around recursion just yet :)

A fiddle prepared with some test data can be found here: jsFiddle. The fiddle uses angular for some simple databinding and debugging the result output and underscorejs for handling the arrays.

I'm trying to get a result looking something like this: Miniors | Boys | 54kg - 62kg where every value delimited by a pipe | es from an array containing a certain "type of restriction". For example: ageGroups, genders, weightClasses (as seen above).

The way I'm able to get this result right now is if I hard code the nested forEach-loops (using underscorejs), but this means I have to now how many arrays I have to loop over to get wanted result. This works "fine":

var categories = [];
_.each(ageGroups, function(ageGroup) {
   _.each(gender, function(gender) {
     _.each(weightClasses, function(weightClass) {
       categories.push(ageGroup.name + ' | ' + gender.name + ' | ' + weightClass.name);
      });
   });
});

The output is an array (categories) with all the possible binations of the restriction arrays.

Now, my problem is that I need a way to do the same with an unknown number of restriction arrays. My guess for a proper solution is recursion, BUT I haven't been able to produce anything that actually works since I'm not able to wrap my head around recursion just yet :)

A fiddle prepared with some test data can be found here: jsFiddle. The fiddle uses angular for some simple databinding and debugging the result output and underscorejs for handling the arrays.

• javascript
• arrays
• recursion
• underscore.js
• nested-loops

Share Improve this question Follow edited Nov 2, 2014 at 20:08 David G 96.9k4141 gold badges172172 silver badges257257 bronze badges asked Nov 2, 2014 at 19:59 aupaup 81077 silver badges1919 bronze badges 3

• Try not to use side-effects (i.e. pushing to a global categories array), but instead return from each step and use map (and flatten) – Bergi Commented Nov 2, 2014 at 20:32
• Hmm.. Okey. Flatten wont be of any use here since I need a bination of the different values from the different arrays. But map might be something.. Even though I can't see how it would solve the problem I'm facing with a dynamic amount of arrays. You care to elaborate? – aup Commented Nov 2, 2014 at 20:43
• Try to use map (even in a non-generic way) and you will see what you need the flatten for. Then, make a function that takes the groups, the current group's index (the "nesting level") and the current names of the visited groups. The base case (when the level of nesting has reached the length of the groups) would then return those current names (joined by ` | `), the recursive case - you'll figure out. – Bergi Commented Nov 2, 2014 at 20:55

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 5

I recently wrote a recursive function to create all binations of arrays. You would have to translate your data into an array of arrays that my function uses, but that shouldn't be difficult.

Anyway, here's the code with a runnable example:

var v = [['Miniors','Kadettes','Juniors', 'Seniors'], ['Boys','Girls','Men','Women'],['54kg - 62kg','64kg - 70kg','71kg - 78kg','79kg - 84kg']];
var bos = createCombinations(v);
for(var i = 0; i < bos.length; i++) {
  document.getElementsByTagName("body")[0].innerHTML += bos[i] + "<br/>";
}

function createCombinations(fields, currentCombinations) {
  //prevent side-effects
  var tempFields = fields.slice();

  //recursively build a list binations
  var delimiter = ' | ';
  if (!tempFields || tempFields.length == 0) {
    return currentCombinations;
  }
  else {
    var binations = [];
    var field = tempFields.pop();

    for (var valueIndex = 0; valueIndex < field.length; valueIndex++) {
      var valueName = field[valueIndex];

      if (!currentCombinations || currentCombinations.length == 0) {
        var binationName = valueName;
        binations.push(binationName);
      }
      else {
        for (var binationIndex = 0; binationIndex < currentCombinations.length; binationIndex++) {
          var currentCombination = currentCombinations[binationIndex];
          var binationName = valueName + delimiter + currentCombination;
          binations.push(binationName);
        }
      }
    }
    return createCombinations(tempFields, binations);
  }
}

function iterate(lists, fn)
{
  var values = [];
  function process(listIndex)
  {
    var list = lists[listIndex];

    // no list? create the value
    if (!list)
    {
      fn.apply(null, values);
      return;
    }

    for (var i = 0; i < list.length; i++)
    {
      values[listIndex] = list[i];
      process(listIndex+1);
    }
  }

  process(0);
}

here is a working example based on the data mentioned in your question: http://jsbin./boqucu/2/edit

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