How to change one column in 2d array by mapping function in google scripts?

Question

I've an array which I got from a spreadsheet by .getValues() method:

var arr = [
[12, 123euro, 13],
[345, 432euro, 293],
]

I want to remove 'eur' by mapping like this:

var newarr = arr.map(row => row[1].replace('euro',''))

But this gives me:

[123, 432]

Rewriting the line as:

newarr = arr.map(row => [row[0], row[1].replace('euro',''), row[2])

gives me the desired newarr:

var arr = [
[12, 123euro, 13],
[345, 432euro, 293],
]

I was expecting this result from the first try. What am I missing?

In your first try you are returning a single element per row and that is row[1].replace('euro',''). — Marios
– Marios, Commented Mar 9, 2021 at 23:05

pilchard · Accepted Answer · 2021-03-09 21:57:48Z

5

Array.prototype.map() expects a single return value from each iteration which is assigned to the index of that iteration in the array on which it is called.

Your first attempt arr.map(row => row[1].replace('euro','')) returns the return value of your .replace() call, which is a string, and replaces the entire iterated row with it.

Instead, you want to assign that returned value back to row[1] and then return the entire row. (Here using a comma operator and converting the returned string to an integer using a unary plus(+)).

arr.map(row => (row[1] = +row[1].replace('euro', ''), row))

It should be noted that mutating the row array this way will also mutate the original. To avoid this you'll need to make a copy, either with slice() or by using spread syntax (or by building an entirely new array as you did in your working example).

var arr = [
  [12, '123euro', 13],
  [345, '432euro', 293],
];

var newarr = arr.map(row => {
  const newRow = [...row];
  newRow[1] = +newRow[1].replace('euro', '');
  return newRow;
})

console.log(newarr);

edited Mar 9, 2021 at 21:57

answered Mar 9, 2021 at 21:45

pilchard

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3 Comments

Andrew Anderson Over a year ago

That works, thank you! Can you please explain the outer parenthesis? (row[1] = +row[1].replace(curToken,''), row) and this part: , row

pilchard Over a year ago

It wraps the two expressions which are separated by the comma operator in order to implicitly return the result after all are evaluated. It is equivalent to arr.map(row => { row[1] = +row[1].replace('euro', ''); return row; }); using a multiline callback with an explicit return value.

Andrew Anderson Over a year ago

I want to know more about this interesting syntax. What should I search for in, say, MDN?

Cooper · Accepted Answer · 2021-03-09 23:03:37Z

0

function myfunc() {
  var arr = [
    [12, '123euro', 13],
    [345, '432euro', 293]
  ];
  let arr1 = arr.map((r) => {
    return [r[0], r[1].replace(/euro/g, ''), r[2]];
  });
  Logger.log(arr1);
}

Execution log
4:07:32 PM  Notice  Execution started
4:07:32 PM  Info    [[12.0, 123, 13.0], [345.0, 432, 293.0]]
4:07:32 PM  Notice  Execution completed

answered Mar 9, 2021 at 23:03

Cooper

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