CODEWITHSUNDEEP
julia
Alec
Alec

Reputation: 4482

How to round to nearest multiple?

Is there an idiomatic way to round to the nearest multiple of a number?

number   multiple    result
12.2       0.5        12.0
12.2       0.25       12.25
12.4       0.5        12.5

Upvotes: 7

Views: 1024

Answers (1)

ahnlabb
ahnlabb

Reputation: 2162

You can define a function:

round_step(x, step) = round(x / step) * step

Usage:

julia> round_step(12.2, 0.25)
12.25

Such a function is actually used internally in Base for rounding numbers to a certain number of digits in a certain base:

julia> Base._round_step(12.2, 0.25, RoundNearest)
12.25

However since this is an internal implementation detail you shouldn't rely on this function. This function in turn calls _round_invstep.

julia> Base._round_invstep(12.2, 4, RoundNearest)
12.25

julia> Base._round_invstep(12.4, 2, RoundNearest)
12.5

Which performs the operation round(x * invstep, r) / invstep.

Because your examples happen to correspond to 0.1 in base 4 and base 2 you can also use round directly for these particular cases:

julia> round(12.2; base=2, digits=1)
12.0

julia> round(12.2; base=4, digits=1)
12.25

julia> round(12.4; base=2, digits=1)
12.5

Upvotes: 12

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