How to iterate over a dictionary of arrays (without knowing the key name)

Question

I have a an object that looks similar to this:

[
    {"key1": ["2019-04-12-14:54:29.190", "19", "0", "4325", "1"]},
    {"key2": ["2019-04-12-14:54:29.191", "20", "0", "2212", "1"]},
    {"key3": ["2019-04-12-14:54:29.192", "22", "0", "4376", "0"]}
]

However I do NOT know the names of the keys (ie key1, key2 and key3 names are not known to me).

This post is almost exactly what I want, except that method requires you to know the names of the keys.

I need to be able to iterate over the key name and it's value array.

I've tried this:

for (var i in zk) {
    for (var j in zk[i]) {
        console.log(j)
    }
}

But that only prints the key names. How can I iterate through the list as well? In most langues iterating over j seems the logical choice but not in this case. Any ideas? Thank you.

`zk[i][j]` is the array ? But you should actually change your datastructure, either use an array of objects or one object with keys for lookup, not both. — Jonas Wilms, Apr 12 '19 at 21:01
You can use for..of to iterate through values instead of keys https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of — nucleartux, Apr 12 '19 at 21:02
`thing.map(Object.values)` or `thing.flatMap(Object.values)` or `thing.flatMap(Object.values).flat()` depending on how exactly you want it. — georg, Apr 12 '19 at 21:16

wentjun · Accepted Answer · 2019-04-12T21:23:28.647

Let's continue from the code sample you have provided.

1) Getting the keys of each element

for (let i in zk) {
  for (let j in zk[i]) {
    console.log(j)
  }
}

2) Getting the list within each element

for (let i in zk) {
  for (let j in zk[i]) {
    console.log(zk[i][j])
  }
}

3) Iterating through each list within each element

for (let i in zk) {
  for (let j in zk[i]) {
    for (let k = 0; k < zk[i][j].length; k++) {
      console.log(zk[i][j][k])
    }
  }
}

Alternatively, you can use Object.values, which returns the values of each key-value pair. You can consider using Array.map() too.

for (let i in zk) {
  Object.values(zk[i]).map(list => {
    list.map(element => {
      console.log(element);
    });
  });
}

score 1 · Answer 2 · answered Apr 12 '19 at 21:04

1

You missed the object of which value has to be printed

for (var i in zk) {
    for (var j in zk[i]) {
        console.log(zk[i][j])
    }
}

answered Apr 12 '19 at 21:04

vaku

697
8
17

score 1 · Answer 3 · answered Apr 12 '19 at 21:13

The issue is that you're missing one level of your loop. You have to loop over the outer array, then loop over the keys in each object, then if that key's value is an array loop over that array.

If for example you want to log all the values then you can use Object.prototype.keys() it returns an array of the keys in an object so you can try something like this:

const arr = [
        {"key1": ["2019-04-12-14:54:29.190", "19", "0", "4325", "1"]},
        {"key2": ["2019-04-12-14:54:29.191", "20", "0", "2212", "1"]},
        {"key3": ["2019-04-12-14:54:29.192", "22", "0", "4376", "0"]}
    ];

    arr.forEach(x => {
      Object.keys(x).forEach(k => {
        if (Array.isArray(x[k])) {
          x[k].forEach(v => {
            console.log(v);
          });
        } else {
          console.log(x[k]);
        }
      });
    });

score 1 · Answer 4 · answered Apr 12 '19 at 21:19

You could take a differetn approach for iterating the given arrays and objects, with

Array#forEach for iterating an array,
Object.entries for getting an array of arrays with keys and values and a
destructuring assignment for an array of key/value pairs.

var data = [{ key1: ["2019-04-12-14:54:29.190", "19", "0", "4325", "1"] }, { key2: ["2019-04-12-14:54:29.191", "20", "0", "2212", "1"] }, { key3: ["2019-04-12-14:54:29.192", "22", "0", "4376", "0"] }];

data.forEach((object, outerIndex) =>
    Object.entries(object).forEach(([key, array]) => 
        array.forEach((value, innerIndex) => 
            console.log(outerIndex, key, innerIndex, value)
        )
    )
);

.as-console-wrapper { max-height: 100% !important; top: 0; }

benvc · Answer 5 · 2021-09-29T18:55:25.907

Object.entries would be helpful if you are trying to iterate over and output each object key and each of the values in the corresponding array. There are more compact ways to do this, but the nested loops should clearly illustrate what is happening.

const arr = [
  {"key1": ["2019-04-12-14:54:29.190", "19", "0", "4325", "1"]},
  {"key2": ["2019-04-12-14:54:29.191", "20", "0", "2212", "1"]},
  {"key3": ["2019-04-12-14:54:29.192", "22", "0", "4376", "0"]}
];

for (const obj of arr) {
  for (const [key, values] of Object.entries(obj)) {
    console.log(`KEY: ${key}`);
    console.log('VALUES: ');
    for (const value of values) {
      console.log(value);
    }
  }
}
// Example output from first object...
// KEY: key1
// VALUES: 
// 2019-04-12-14:54:29.190
// 19
// 0
// 4325
// 1

score 0 · Answer 6 · answered Apr 12 '19 at 21:08

In js you always get the keys so what you do is:

for (var i in zk) {
    for (var j in zk[i]) { // j wil ben key1, key2 ect
        console.log(zk[i][j]); // arrays  ["2019-04-12-14:54:29.190", "19", "0", "4325", "1"] over where you can itterate
        for (var k in zk[i][j]) {
            console.log(zk[i][j][k]); // "2019-04-12-14:54:29.190" ect
        }
    }
}

score 0 · Answer 7 · answered Apr 12 '19 at 21:08

Use Object.values:

const arr = [
    {"key1": ["2019-04-12-14:54:29.190", "19", "0", "4325", "1"]},
    {"key2": ["2019-04-12-14:54:29.191", "20", "0", "2212", "1"]},
    {"key3": ["2019-04-12-14:54:29.192", "22", "0", "4376", "0"]}
];

arr.forEach(obj => console.log(Object.values(obj)));

.as-console-wrapper { max-height: 100% !important; top: auto; }

How to iterate over a dictionary of arrays (without knowing the key name)

7 Answers7