Increment a parameter in a javascript recursive function

Question

I have the following data stored in a variable:

let categories = [
    {
    name: "a",
    selected: false,
    nodes: [
        {
        name: "aa",
        selected: false
      },
      {
        name: "ab",
        selected: true
      },
      {
        name: "ac",
        selected: true
      },
      {
        name: "ad",
        selected: false
      }
    ]
  },
  {
    name: "b",
    selected: false,
    nodes: [
        {
        name: "ba",
        selected: false
      },
      {
        name: "bb",
        selected: true
      },
      {
        name: "bc",
        selected: true
      },
      {
        name: "bd",
        selected: false
      }
    ]
  }
];

I want to count how much item has selected = true.
So I create the following function:

function getSelected(categories, counter = 0) {
    for (let index = 0; index < categories.length; index++) {
        const category = categories[index];
    if (category.selected) {
        counter++;
    }
    if (category.nodes && category.nodes.length) {
        category.nodes.forEach(cat => getSelected([cat], counter));
    }
    }
  return counter;
}

but it always returns 0.

A working jsFiddle

Nina Scholz · Accepted Answer · 2019-12-26 14:16:54Z

3

You could take a recursive reduce of the nodes and count selected.

const
    countSelected = (s, o) => (o.nodes || []).reduce(countSelected, s + o.selected);

let categories = [{ name: "a", selected: false, nodes: [{ name: "aa", selected: false }, { name: "ab", selected: true }, { name: "ac", selected: true }, { name: "ad", selected: false }] }, { name: "b", selected: false, nodes: [{ name: "ba", selected: false }, { name: "bb", selected: true }, { name: "bc", selected: true }, { name: "bd", selected: false }] }],
    count = categories.reduce(countSelected, 0);

console.log(count);

answered Dec 26, 2019 at 14:16

Nina Scholz

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2 Comments

Ayoub k Over a year ago

PS: the depth of nodes is unknown, so reduce won't work if we had deeper nodes.

Nina Scholz Over a year ago

it works here for all nested nodes properties, because is uses a recursion. please have a look to the reduce of countSelected.

jonatjano · Accepted Answer · 2019-12-26 14:18:25Z

It is because Number (and other primitives) arguments to function are duplicated, it create a whole new variable initialized with the arguments value.

what you can do is either use the return value of your function and sum it, or you can use Objects as arguments as they are send by reference, so you keep the same object :

let categories = [{name: "a",selected: false,nodes: [{name: "aa",selected: false},{name: "ab",selected: true},{name: "ac",selected: true},{name: "ad",selected: false}]},{name: "b",selected: false,nodes: [{name: "ba",selected: false},{name: "bb",selected: true},{name: "bc",selected: true},{name: "bd",selected: false}]}]

function getSelectedWithObject(categories, counter = {val: 0}) {
    for (let index = 0; index < categories.length; index++) {
        const category = categories[index]
        if (category.selected) {
            counter.val++
        }
        if (category.nodes && category.nodes.length) {
            category.nodes.forEach(cat => getSelectedWithObject([cat], counter))
        }
    }
    return counter.val
}

function getSelectedWithReturnValue(categories) {
    let counter = 0
    for (let index = 0; index < categories.length; index++) {
        const category = categories[index]
        if (category.selected) {
            counter++
        }
        if (category.nodes && category.nodes.length) {
            category.nodes.forEach(cat => counter += getSelectedWithReturnValue([cat]))
        }
    }
    return counter
}

console.log(getSelectedWithObject(categories))
console.log(getSelectedWithReturnValue(categories))

Omar Mneimneh · Accepted Answer · 2019-12-26 14:17:45Z

1

counter is an integer so it's passed by value here. Make the counter the result you want to get back from the function and there you go:

function getSelected(categories) {
    var counter = 0;
    for (let index = 0; index < categories.length; index++) {
        const category = categories[index];
        if (category.selected) {
           counter++;
        }
        if (category.nodes && category.nodes.length) {
           category.nodes.forEach(cat => counter += getSelected([cat]));
        }
    }
    return counter;
}

console.log(getSelected(categories));

answered Dec 26, 2019 at 14:17

Omar Mneimneh

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