Reference · Vectors

vec.diff

vec.diff(list | null) -> list

What it does

The difference between each item and the one before it: a list one shorter than the input, where item i is xs[i + 1] - xs[i]. Ints stay ints and floats stay floats, as with -.

Examples

print(vec.diff([1, 4, 9, 16]))print(vec.diff([5, 3, 8]))print(vec.diff([1.5, 1]))

[3, 5, 7][-2, 5][-0.5]

Edge cases

• The empty list, one item, or null gives the empty list.
• A fall gives a negative number; the sign says the direction.
• vec.diff undoes vec.cumsum from the second item on.

print(vec.diff([]), vec.diff([1]), vec.diff(null))print(vec.diff([10, 7]))print(vec.diff(vec.cumsum([3, 5, 4])))

[] [] [][-3][5, 4]

Errors

An item that is not an int or a float, or an argument that is not a list, is a runtime error, not an error value. A decimal is not accepted; convert with float.

print(vec.diff([1, "a"]))

line 1: `vec.diff` expects numbers, got str and int

Chaining

The day-to-day change of a series, and its largest jump:

let sales = [3, 5, 4, 6, 8]print(sales | vec.diff)print(sales | vec.diff | vec.abs | max)

[2, -1, 2, 2]2

See also

vec.cumsum, vec.sub, vec.abs, vec.rolling_mean

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