reduce(
@array: [any],
initial: any,
f: fn(any, accum: any): any,
): any
Take a starting value. Then, for each element of an array, calculate the next value, using the previous value and the element.
Arguments
| Name | Type | Description | Required |
|---|---|---|---|
array | [any] | Each element of this array gets run through the function f, combined with the previous output from f, and then used for the next run. | Yes |
initial | any | The first time f is run, it will be called with the first item of array and this initial starting value. | Yes |
f | fn(any, accum: any): any | Run once per item in the input array. This function takes an item from the array, and the previous output from f (or initial on the very first run). The final time f is run, its output is returned as the final output from reduce. | Yes |
Returns
Examples
// This function adds two numbers.
fn add(@a, accum) { return a + accum }
// This function adds an array of numbers.
// It uses the `reduce` function, to call the `add` function on every
// element of the `arr` parameter. The starting value is 0.
fn sum(@arr) { return reduce(arr, initial = 0, f = add) }
/*
The above is basically like this pseudo-code:
fn sum(arr):
sumSoFar = 0
for i in arr:
sumSoFar = add(i, sumSoFar)
return sumSoFar
*/
// We use `assert` to check that our `sum` function gives the
// expected result. It's good to check your work!
assert(sum([1, 2, 3]), isEqualTo = 6, tolerance = 0.1, error = "1 + 2 + 3 summed is 6")
// This example works just like the previous example above, but it uses
// an anonymous `add` function as its parameter, instead of declaring a
// named function outside.
arr = [1, 2, 3]
sum = reduce(arr, initial = 0, f = fn (@i, accum) { return i + accum })
// We use `assert` to check that our `sum` function gives the
// expected result. It's good to check your work!
assert(sum, isEqualTo = 6, tolerance = 0.1, error = "1 + 2 + 3 summed is 6")
// Declare a function that sketches a decagon.
fn decagon(@radius) {
// Each side of the decagon is turned this many radians from the previous angle.
stepAngle = ((1/10) * TAU): number(rad)
// Start the decagon sketch at this point.
startOfDecagonSketch = startSketchOn(XY)
|> startProfile(at = [(cos(0)*radius), (sin(0) * radius)])
// Use a `reduce` to draw the remaining decagon sides.
// For each number in the array 1..10, run the given function,
// which takes a partially-sketched decagon and adds one more edge to it.
fullDecagon = reduce([1..10], initial = startOfDecagonSketch, f = fn(@i, accum) {
// Draw one edge of the decagon.
x = cos(stepAngle * i) * radius
y = sin(stepAngle * i) * radius
return line(accum, end = [x, y])
})
return fullDecagon
}
/*
The `decagon` above is basically like this pseudo-code:
fn decagon(radius):
stepAngle = ((1/10) * TAU): number(rad)
plane = startSketchOn(XY)
startOfDecagonSketch = startProfile(plane, at = [(cos(0)*radius), (sin(0) * radius)])
// Here's the reduce part.
partialDecagon = startOfDecagonSketch
for i in [1..10]:
x = cos(stepAngle * i) * radius
y = sin(stepAngle * i) * radius
partialDecagon = line(partialDecagon, end = [x, y])
fullDecagon = partialDecagon // it's now full
return fullDecagon
*/
// Use the `decagon` function declared above, to sketch a decagon with radius 5.
decagon(5.0) |> close()
