Summing data in array of arrays in Javascript

Question

I have the following array:

var myData = [
[7106.86000000, 5],
[7107.34000000, 2],
[7107.55000000, 10],
[7107.58000000, 3],
[7107.67000000, 90],
.....
]

I need to generate a new array where, on the second element of every row, i need to have the sum of the second element of the previous row, here is the desidered output:

var newData = [
[7106.86000000, 5],
[7107.34000000, 7],
[7107.55000000, 17],
[7107.58000000, 20],
[7107.67000000, 110],
.....
]

Since 5+2=7, 7+10=17 and so on.

Now i now how to do that with a normal array of elements, where i would have used reduce, but i don't know how to handle this with an array of arrays where i need to perform this operation only on the second element of every subarray. What can i use in this case? I was going to use a nested loop but it doesn't look like the most efficient way to do that, since this code will be executed on browser

Nina Scholz · Accepted Answer · 2020-04-23 18:18:11Z

1

Just take a closure over the sum and map the values while updating the sum with the right part.

var data = [[7106.86000000, 5], [7107.34000000, 2], [7107.55000000, 10], [7107.58000000, 3], [7107.67000000, 90]],
    result = data.map((sum => ([l, r]) => [l, sum += r])(0));

console.log(result);

answered Apr 23, 2020 at 18:18

Nina Scholz

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1 Comment

All01 Over a year ago

Thank you a lot! This seems to be the best way to go! Give me 9 minutes to accept your answer!

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