I was prototyping: julia> a=[1,2,3,1,2]
julia> b=[a[i]<a[i+1] for i in 1:length(a)-1] 4-element Array{Bool,1}: true true false true In the beginning when trying stuff out I used: for i in a[1:end-1] or for i in a[2:end] and it got me thinking, end-1 works for any kind of array, but 1 as the start (or 2) is not correct in general. For e.g. general (e.g. zero-based arrays now allowed), what do you do? [If I need all: for i in a just works] In the beginning, because of error, there seemed to be no bounds checking, but since it's there, is there a way do disable? julia> b=[@inbounds a[i]<a[i+1] for i in 1:length(a)-1] 4-element Array{Void,1}: nothing nothing nothing nothing julia> b=[(@inbounds (a[i]<a[i+1]) for i in 1:length(a)-1)] 1-element Array{Base.Generator{UnitRange{Int64},##59#60},1}: Base.Generator{UnitRange{Int64},##59#60}(#59,1:4) Eventually I want something different, the points where, increasing turn to decreasing (or vice versa), at most n/2 points. Array comprehension is probably not the right way, as I need to know how many point. I'll change to a loop (that will be itself in a loop), that uses a preallocated array for result, I want to reuse that in each iteration of the outer loop; I assume that isn't possible with an array comprehension.