b816df21d2
* Deprecate startSketchAt() stdlib function * Remove uses of startSketchAt() from the doc tests * Update docs
122 lines
92 KiB
Markdown
122 lines
92 KiB
Markdown
---
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title: "reduce"
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excerpt: "Take a starting value. Then, for each element of an array, calculate the next value,"
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layout: manual
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---
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Take a starting value. Then, for each element of an array, calculate the next value,
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using the previous value and the element.
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```js
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reduce(array: [KclValue], start: KclValue, reduce_fn: FunctionParam) -> KclValue
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```
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### Arguments
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| Name | Type | Description | Required |
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|----------|------|-------------|----------|
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| `array` | [`[KclValue]`](/docs/kcl/types/KclValue) | | Yes |
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| `start` | [`KclValue`](/docs/kcl/types/KclValue) | Any KCL value. | Yes |
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| `reduce_fn` | `FunctionParam` | | Yes |
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### Returns
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[`KclValue`](/docs/kcl/types/KclValue) - Any KCL value.
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### Examples
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```js
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// This function adds two numbers.
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fn add(a, b) {
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return a + b
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}
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// This function adds an array of numbers.
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// It uses the `reduce` function, to call the `add` function on every
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// element of the `arr` parameter. The starting value is 0.
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fn sum(arr) {
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return reduce(arr, 0, add)
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}
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/* The above is basically like this pseudo-code:
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fn sum(arr):
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sumSoFar = 0
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for i in arr:
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sumSoFar = add(sumSoFar, i)
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return sumSoFar */
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// We use `assertEqual` to check that our `sum` function gives the
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// expected result. It's good to check your work!
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assertEqual(sum([1, 2, 3]), 6, 0.00001, "1 + 2 + 3 summed is 6")
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```
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```js
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// This example works just like the previous example above, but it uses
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// an anonymous `add` function as its parameter, instead of declaring a
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// named function outside.
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arr = [1, 2, 3]
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sum = reduce(arr, 0, fn(i, result_so_far) {
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return i + result_so_far
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})
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// We use `assertEqual` to check that our `sum` function gives the
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// expected result. It's good to check your work!
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assertEqual(sum, 6, 0.00001, "1 + 2 + 3 summed is 6")
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```
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```js
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// Declare a function that sketches a decagon.
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fn decagon(radius) {
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// Each side of the decagon is turned this many degrees from the previous angle.
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stepAngle = 1 / 10 * tau()
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// Start the decagon sketch at this point.
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startOfDecagonSketch = startSketchOn('XY')
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|> startProfileAt([cos(0) * radius, sin(0) * radius], %)
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// Use a `reduce` to draw the remaining decagon sides.
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// For each number in the array 1..10, run the given function,
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// which takes a partially-sketched decagon and adds one more edge to it.
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fullDecagon = reduce([1..10], startOfDecagonSketch, fn(i, partialDecagon) {
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// Draw one edge of the decagon.
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x = cos(stepAngle * i) * radius
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y = sin(stepAngle * i) * radius
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return lineTo([x, y], partialDecagon)
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})
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return fullDecagon
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}
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/* The `decagon` above is basically like this pseudo-code:
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fn decagon(radius):
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stepAngle = (1/10) * tau()
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plane = startSketchOn('XY')
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startOfDecagonSketch = startProfileAt([(cos(0)*radius), (sin(0) * radius)], plane)
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// Here's the reduce part.
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partialDecagon = startOfDecagonSketch
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for i in [1..10]:
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x = cos(stepAngle * i) * radius
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y = sin(stepAngle * i) * radius
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partialDecagon = lineTo([x, y], partialDecagon)
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fullDecagon = partialDecagon // it's now full
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return fullDecagon */
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// Use the `decagon` function declared above, to sketch a decagon with radius 5.
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decagon(5.0)
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|> close(%)
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```
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