Utilizing the .reduce method on an object with an array of values in order to transform it into an

Question

Utilizing the .reduce method on an object with an array of values in order to transform it into an

I am attempting to transform an object with arrays as properties into a single array containing all elements from these nested arrays.

My approach is as follows:

data1 = [{
  a: 1,
  b: ["uz", "vy"]
}, {
  a: 2,
  b: ["wxa", "xwy"]
}, {
  a: 6,
  b: ["ysa", "zaa"]
}]

data1.reduce(function(q, w) {
  return q.b.concat(w.b)
})

The desired output should be:

data1 = ["uz","vy","wxa","xwy","ysa","zaa"]

However, I encounter the following error message:

"Uncaught TypeError: Cannot read property 'concat' of undefined"

If q.b references an array within an object, why does it not have the property concat? Where did I make a mistake in this code?

javascript arrays object reduce

Answer 1

Answer №1

You received an error because the variable q is an array and does not have a property b. Additionally, you forgot to include the initial value.

To resolve this issue, you can use concat and map.

let data1 = [{a: 1,b: ["uz", "vy"]}, {a: 2,b: ["wxa", "xwy"]}, {a: 6,b: ["ysa", "zaa"]}];

let result = [].concat(...data1.map(o => o.b));

console.log(result);

If you prefer to utilize reduce, follow these steps:

let data1 = [{a: 1,b: ["uz", "vy"]}, {a: 2,b: ["wxa", "xwy"]}, {a: 6,b: ["ysa", "zaa"]}];

let result = data1.reduce(function(q, w) {
  return q.concat(w.b);
}, []); //<-- Include [] as the initial value

console.log(result);

Answer 2

You received an error because the variable q is an array and does not have a property b. Additionally, you forgot to include the initial value.

To resolve this issue, you can use concat and map.

let data1 = [{a: 1,b: ["uz", "vy"]}, {a: 2,b: ["wxa", "xwy"]}, {a: 6,b: ["ysa", "zaa"]}];

let result = [].concat(...data1.map(o => o.b));

console.log(result);

If you prefer to utilize reduce, follow these steps:

let data1 = [{a: 1,b: ["uz", "vy"]}, {a: 2,b: ["wxa", "xwy"]}, {a: 6,b: ["ysa", "zaa"]}];

let result = data1.reduce(function(q, w) {
  return q.concat(w.b);
}, []); //<-- Include [] as the initial value

console.log(result);

Answer 3

Answer №2

To properly use the reduce function, make sure to provide an initial value. Additionally, in the first call, ensure that you concatenate to q instead of trying to access q.b:

data2 = [{
  a: 5,
  b: ["xyz", "abc"]
}, {
  a: 3,
  b: ["lmn", "def"]
}, {
  a: 8,
  b: ["pqr", "ghi"]
}]

var output = data2.reduce(function(q, w) {
  return q.concat(w.b);
}, [])

console.log(output);

Answer 4

To properly use the reduce function, make sure to provide an initial value. Additionally, in the first call, ensure that you concatenate to q instead of trying to access q.b:

data2 = [{
  a: 5,
  b: ["xyz", "abc"]
}, {
  a: 3,
  b: ["lmn", "def"]
}, {
  a: 8,
  b: ["pqr", "ghi"]
}]

var output = data2.reduce(function(q, w) {
  return q.concat(w.b);
}, [])

console.log(output);

Utilizing the .reduce method on an object with an array of values in order to transform it into an

Answer №1

Answer №2

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