There's the function mod1 which does exactly the shifting by 1 that you
need.
On Mon, Apr 28, 2014, at 3:22, Tomas Lycken wrote:
...and of course my Julia example didn't really work out. Because of
operator precedence, I actually need v[((i+1) % (N-1)) + 1] in the
last example, making the need for a better idiom for this kind of
looping even greater. My eyes are bleeding...
// T
On Monday, April 28, 2014 11:57:09 AM UTC+2, Tomas Lycken wrote:
In languages with zero-indexed vectors, I can easily let my indices
"wrap" by taking a modulus:
N = length(v)
for i = 0:N-1
v[i+1 % N] = ...
end
will loop from the second element to the last, and then take the first,
since N % N == 0. However, with Julia's 1-indexed arrays, it's not that
easy - at some point, I'll end up at index 0:
N = length(v)
for i = 1:N
v[i + 1 % N] = ... # breaks at i = N-1, since index then becomes 0
end
I could first offset my entire loop index by one, take the modulus, and
then add one again:
N = length(v)
for i = 0:N-1
v[(i+1 % N) + 1] = ...
end
but this seems clunky to me, and is difficult to understand at first
glance (maybe not to current me, but to me-in-a-month trying to figure
out what this code does...). Is there a more idiomatic way to do the
same thing in Julia?
My actual problem is having a (sorted) list of vertices in a polygon,
and wanting to loop over the edges (i.e. adjacent pairs in the list),
so in each step I want to access something like v[i+1]-v[i] and have
the end-points close the loop.
Thanks in advance,
// T
