How to loop through an object of arrays in Javascript?

Question

For the below code,

const groupbysubject = {
                    "Mathematics":
                    [
                      {totalStudents: "23", average: "78", class: "2"},
                      {totalStudents: "25", average: "80", class: "3"}
                    ],
                    "English":
                    [
                      {totalStudents: "33", average: "98", class: "2"},
                      {totalStudents: "35", average: "99", class: "3"}
                    ],
                    "Science":
                    [
                      {totalStudents: "43", average: "65", class: "2"},
                    ]
                  }

                

var isEnglishPresent = Object.fromEntries(
                           Object.entries(groupbysubject).filter(
                             ([key, val])=> key.includes("English")
                            )
                        );

I want the following output :

"33" "98" "2" "35" "99" "3"

I have filtered the above groupbysubject object into isEnglishPresent object. How do I proceed further to iterate over isEnglishPresent and get the above output. Please help

Thank you.

Tomalak · Accepted Answer · 2022-05-05 06:03:49Z

4

You want a flat list of the values from the items inside the English key:

const groupbysubject = {
  "Mathematics":
  [
    {totalStudents: "23", average: "78", class: "2"},
    {totalStudents: "25", average: "80", class: "3"}
  ],
  "English":
  [
    {totalStudents: "33", average: "98", class: "2"},
    {totalStudents: "35", average: "99", class: "3"}
  ],
  "Science":
  [
    {totalStudents: "43", average: "65", class: "2"},
  ]
};

var englishData = groupbysubject.English.flatMap(item => Object.values(item));

console.log(englishData);

answered May 5, 2022 at 6:03

Tomalak

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5 Comments

user13692230 Over a year ago

Thank you but what if the in the output we only need totalStudents of English. How will we do that then?

Tomalak Over a year ago

@ApoorvaOjha Why did your question not say from the start what you need?

Tomalak Over a year ago

Also, read my code, understand what it does, experiment a little, and you will figure it out. You don't depend on me making it copy-and-paste ready for you.

Andus Over a year ago

Although my answer is being accepted, I appreciate this less code flatMap approach

Tomalak Over a year ago

@Andus It's a moot point anyway, as it only solves the problem the OP asked for, not the problem the OP wanted to solve.

Andus · Accepted Answer · 2022-05-05 06:05:19Z

0

Assume you have an English array with N objects like below.

const English = [
  {totalStudents: "33", average: "98", class: "2"},
  {totalStudents: "35", average: "99", class: "3"},
  ...
]

Here's how you extract all the values and put it into an array.

English.map(item => Object.values(item)).flat()

Here's the output

["33", "98", "2", "35", "99", "3"]

answered May 5, 2022 at 6:05

Andus

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1 Comment

Roko C. Buljan Over a year ago

Instead of .map() followed by .flat() there's the Array.prototype.flatMap()

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