42 lines
1.3 KiB
Markdown
42 lines
1.3 KiB
Markdown
---
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title: JSON to CSV
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tags: array,string,object
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expertise: advanced
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cover: blog_images/horse-sunset.jpg
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firstSeen: 2018-07-06T20:25:46+03:00
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lastUpdated: 2021-10-13T19:29:39+02:00
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---
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Converts an array of objects to a comma-separated values (CSV) string that contains only the `columns` specified.
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- Use `Array.prototype.join()` to combine all the names in `columns` to create the first row, using the provided `delimiter`.
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- Use `Array.prototype.map()` and `Array.prototype.reduce()` to create a row for each object. Substitute non-existent values with empty strings and only mapping values in `columns`.
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- Use `Array.prototype.join()` to combine all rows into a string, separating each row with a newline (`\n`).
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- Omit the third argument, `delimiter`, to use a default delimiter of `','`.
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```js
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const JSONtoCSV = (arr, columns, delimiter = ',') =>
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[
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columns.join(delimiter),
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...arr.map(obj =>
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columns.reduce(
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(acc, key) =>
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`${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`,
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''
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)
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),
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].join('\n');
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```
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```js
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JSONtoCSV(
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[{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }],
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['a', 'b']
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); // 'a,b\n"1","2"\n"3","4"\n"6",""\n"","7"'
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JSONtoCSV(
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[{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }],
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['a', 'b'],
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';'
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); // 'a;b\n"1";"2"\n"3";"4"\n"6";""\n"";"7"'
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```
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