You could also use a list comprehension without enumerate: d=[6,5,4,3,2,1,0] n=4 sum(d[ Bool[i<=n && d[i]!=i && d[d[i]]==i for i in 1:length(d)] ] )
>> 18 Coming from numpy, I find this syntax intuitive, aside from the requirement to explicitly set the comprehension type to Bool. On Thursday, June 19, 2014 11:57:04 AM UTC-4, Matt Bauman wrote: > > There's also an open issue about "splitting" or "splatting" of tuples > within function arguments that's very relevant here: Allow tuple > destructuring in formal arguments, > https://github.com/JuliaLang/julia/issues/6614 > > It's a common use case that I run into often, especially with enumerate > and dictionaries. So you're not alone. > > On Thursday, June 19, 2014 3:57:33 AM UTC-4, gentlebeldin wrote: >> >> Ah, I see, multiple dispatch is the real cause. I'll have to live with >> the little ideosyncrasy, then. >> Peter's idea filter(p -> +(p...)%4 != 0, pairs) works fine... in my >> simple example. In real life, I wanted to filter an array d of integers, >> with a predicate >> i<=n && d[i]!=i && d[d[i]]==i, so filter((i,v)->i<=n && v!=i && >> d[v]==i,enumerate(d)) looked like a reasonable idea, it just doesn't work. >> We can make it work, though that looks a bit strange, too: >> filter([e for e in enumerate(d)]) do x >> i,v=x >> i<=n && v!=i && d[v]==i >> end >> Here, it looks as if the function filter took only one argument. It >> works, however. In my code, I had to sum up the values of i after >> filtering, so I chose the obscure formulation >> sum(map(first,filter(x->x[1]!=x[2] && x[2]<=n && >> d[x[2]]==x[1],enumerate(d)))) >> >>> >>>>
