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JavaScript: Convert an array of objects to a comma-separated values string that contains only the columns specified

JavaScript fundamental (ES6 Syntax): Exercise-5 with Solution

Write a JavaScript program to convert an array of objects to a comma-separated values (CSV) string that contains only the columns specified.

  • Use Array.prototype.join(delimiter) to combine all the names in columns to create the first row.
  • Use Array.prototype.map() and Array.prototype.reduce() to create a row for each object, substituting non-existent values with empty strings and only mapping values in columns.
  • Use Array.prototype.join('\n') to combine all rows into a string.
  • Omit the third argument, delimiter, to use a default delimiter of,.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2
const JSON_to_CSV = (arr, columns, delimiter = ',') =>
  [
    columns.join(delimiter),
    ...arr.map(obj =>
      columns.reduce(
        (acc, key) => `${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`,
        ''
      )
    )
  ].join('\n');

console.log(JSON_to_CSV([{ x: 100, y: 200 }, { x: 300, y: 400, z: 500 }, { x: 6 }, { y: 7 }], ['x', 'y']));
console.log(JSON_to_CSV([{ x: 100, y: 200 }, { x: 300, y: 400, z: 500 }, { x: 6 }, { y: 7 }], ['x', 'y'], ';'));

Sample Output:

x,y
"100","200"
"300","400"
"6",""
"","7"
x;y
"100";"200"
"300";"400"
"6";""
"";"7"

Flowchart:

flowchart: Convert an array of objects to a comma-separated values string that contains only the columns specified

Live Demo:

See the Pen javascript-basic-exercise-1-5 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to convert a comma-separated values (CSV) string to a 2D array of objects. The first row of the string is used as the title row.
Next: Write a JavaScript program to target a given value in a nested JSON object, based on the given key.

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JavaScript: Tips of the Day

Chunks an array into n smaller arrays

Example:

const tips_chunkIntoN = (arr, n) => {
  const size = Math.ceil(arr.length / n);
  return Array.from({ length: n }, (v, i) =>
    arr.slice(i * size, i * size + size)
  );
}
console.log(tips_chunkIntoN([1, 2, 3, 4, 5, 6, 7,8], 4));

Output:

[[1,2],[3,4],[5,6],[7,8]]