javascript - Building an array of sequential numbers

Question

i have an incoming array:

[{step: 0, count: 1}, {step: 1, count: 5}, {step: 5, count: 5}] 

so i need to transform incoming array in another array

[0, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30]

I have tried to go this way:

const convertRangeData = (rangeData) =>
  {
  const convertedRangeData =
    rangeData.reduce( (acc, item) => 
        {
        const { step, count } = item;
        const prev                 = acc[acc.length - 1];
        return [...acc, ...[...Array(count)].fill(step).map((i, idx) => i * (idx + 1) + prev)];
        },[0] )
    return convertedRangeData;
  }

but I've got

[0, 0, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30]

question from:https://stackoverflow.com/questions/65849430/building-an-array-of-sequential-numbers

Answer 1

Use Array.from() to create an array with values in the ranges. Then iterate the array of ranges.

To create the continuous ranges reduce the array of ranges. When creating a range take the last number from the accumulator (acc), and use it as the start value.

const range = ({ step, count }, start = 0) => 
  Array.from({ length: count }, (_, i) => (i + 1) * step + start)
  
const continuousRange = arr =>
  arr.reduce((acc, r) => acc.concat(range(r, acc[acc.length -1])), [])

const ranges = [{step: 0, count: 1}, {step: 1, count: 5}, {step: 5, count: 5}]

const result = continuousRange(ranges)

console.log(result)