Hard to put into words but I am looking for a function that takes an array and reduces it down to a given size. The use case is specifying ticks for graph in d3.
const availableDatetimes: Date[] = [...]
const numberOfXTicks = chartWidth / 80
const tickValues = reduceArrSize(availableDatetimes, numberOfXTicks)
the result should have evenly distributed dates
I called it shrinkArray(), because reducing an array is the name of a different well-defined operation. Here it is:
const shrinkArray = (array, size) => {
const step = array.length / size
return array.filter((v, i) => Math.floor(i % step) == 0)
}
Let's shrink an array of size 100 to size 33:
const originalArray = (new Array(100).fill(0)).map((v, i) => i)
const shrunkenArray = shrinkArray(originalArray, 33)
console.log(shrunkenArray);
console.log(shrunkenArray.length == 33);
So:
[
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71,
72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83,
84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95,
96, 97, 98, 99
]
is shrunken to:
[
0, 4, 7, 10, 13, 16, 19, 22, 25,
28, 31, 34, 37, 40, 43, 46, 49, 53,
56, 59, 62, 65, 68, 71, 74, 77, 80,
83, 86, 89, 92, 95, 98
]
that is of size 33.
In this example the array is integers from 0 to 99, but obviously the function works for any data type.