El miércoles, 15 de julio de 2015, 14:03:16 (UTC-5), Mauricio Esteban Cuak
escribió:
>
> Just in case it seems a bit more transparent, this also works:
>
> r = rand(5)
> map( x -> x[1] + x[2], enumerate(r))
>
>
>
I personally find the following array comprehension the most transparent
option:
[i+v for (i,v) in enumerate(r)]
It also has the benefit of being much faster (Julia 0.3.11-pre):
julia> f1(r) = [i+v for (i,v) in enumerate(r)]
f1 (generic function with 1 method)
julia> f2(r) = map( x -> x[1] + x[2], enumerate(r))
f2 (generic function with 1 method)
# warm-up:
r = rand(5)
f1(r)
f2(r);
r = rand(10^6)
julia> @time f1(r);
elapsed time: 0.007597053 seconds (8000144 bytes allocated)
julia> @time f2(r);
elapsed time: 0.313020208 seconds (160753984 bytes allocated, 35.39% gc
time)
>
> El martes, 14 de julio de 2015, 20:20:14 (UTC-5), Yichao Yu escribió:
>>
>> On Tue, Jul 14, 2015 at 7:09 PM, Ritchie Lee <ritch...@gmail.com> wrote:
>> > Sorry if this is a newbie question. I am trying to get map() to work
>> with
>> > with enumerate() but I am getting an error.
>> >
>> > r=rand(5)
>> > map((i,v)->i+v, enumerate(r))
>> > ERROR: wrong number of arguments
>> > in anonymous at none:1
>> > in map at abstractarray.jl:1207
>> >
>> > collect(enumerate(r)) generates an array of 2-tuples as expected.
>>
>> `map` does not splat each element of the iteration and only pass each
>> element as a single argument to the function
>>
>> ```julia
>> julia> r = rand(5)
>> map(x->((i, v) = x; i + v), enumerate(r))
>> 5-element Array{Any,1}:
>> 1.6277
>> 2.41751
>> 3.34848
>> 4.70194
>> 5.89139
>>
>> ```
>>
>> >
>> > Is the syntax incorrect?
>> >
>> > Thanks,
>> >
>> > Ritchie
>>
>
