I was testing some code and noticed something that seemed odd to me when trying to use the range operator (“:”). julia> 1:5 1:5 but julia> 5:1 5:4 I don’t see anything in the help for : that suggests different behavior if a<b or a>b for a:b, although in the help for range I do see this statement…

Note the part about step defaulting to 1. help?> : search: : :: ?: >: <: (:)(start, [step], stop) Range operator. a:b constructs a range from a to b with a step size equal to 1, which produces: • a UnitRange when a and b are integers, or • a StepRange when a and b are characters…

Ah, I see. So 5:-1:1 works just fine. I guess in my head, I only ever think of step sizes as magnitudes, not directions. Guess I’m still used to how R does it. Anyway, thanks for the help!

here some more thoughts on the topic here the code ifelse(stop >= start, stop, convert(T,start-oneunit(stop-start)))

See also related discussions: 'Negative' UnitRange in Julia? The colon punctuation: Why doesn't 5:1 return [5, 4, 3, 2, 1]? Why are empty ranges normalized?

You can also do reverse(1:5) which i think is more readable than 5:-1:1.

Ah, I like that one, thanks. :slight_smile:

You know, this is a common enough error that it would probably be worth explicitly calling out in the docstring. PR: Explicitly call out reverse ranges in `:` docstring by BioTurboNick · Pull Request #53626 · JuliaLang/julia · GitHub

Question about range operator (":")

General Usage

stevengj March 6, 2024, 5:27pm 5

See also related discussions:

'Negative' UnitRange in Julia?
The colon punctuation: Why doesn't 5:1 return [5, 4, 3, 2, 1]?
Why are empty ranges normalized?

Topic		Replies	Views
The colon punctuation: Why doesn't 5:1 return [5, 4, 3, 2, 1]? New to Julia question , range , unitrange	8	1499	December 16, 2023
'Negative' UnitRange in Julia? General Usage	6	1260	December 10, 2021
Reverse UnitRange General Usage	3	627	May 30, 2021
Colon / Ranges New to Julia	5	1952	December 10, 2020
Using step in the range function New to Julia question	1	134	November 20, 2025

Question about range operator (":")

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