Groups   8 of 99+      julia-users › Why does enumerate fail in parallel? 8 posts by 5 authors      Nils Gudat    8 19 15   I just rewrote one of my parallel loops and was surprised by this:    list     a ,  b ,  c      for i in enumerate list      println i    end   1, a     2, b     3, c      addprocs 2      sync  parallel for i in enumerate list      println i    end  ERROR: `getindex` has no method matching getindex ::Enumerate Array ASCIIString,1  , ::UnitRange Int64    Am I doing something wrong here? Is this expected behaviour?     Ismael Venegas Castelló    8 19 15   Enumerate is an iterator, you need to collect the items first:  julia   parallel for i in collect enumerate list              println i         end  julia   From worker 2:   1, a       From worker 2:   2, b       From worker 3:   3, c        Ismael Venegas Castelló    8 19 15   Well that works but it's indeed odd, can you open a new issue for this?      ele... gmail.com    8 20 15     On Thursday, August 20, 2015 at 4:50:49 AM UTC+10, Ismael VC wrote: Well that works but it's indeed odd, can you open a new issue for this?  Not really odd,  parallel needs to divide the set of values between multiple processes, so it needs the whole set of values.      John Brock    8 20 15   This seems issue-worthy if the most recent nightly have the same problem. It looks like Enumerate supports the length property, so the underlying code for  parallel should be able to check the length of the enumerator and figure out how many jobs to assign to each worker.   And regardless of whether it makes sense for  parallel to support enumerate, that error message is pretty opaque -- it doesn't make it obvious to the programmer that parallel doesn't support enumerate, which is a pretty natural thing to try.      John Brock    8 20 15   This seems issue-worthy if the most recent nightly has the same problem. It looks like Enumerate supports the length property, so the underlying code for  parallel should be able to check the length of the enumerator and figure out how many jobs to assign to each worker.   And regardless of whether it makes sense for  parallel to support enumerate, that error message is pretty opaque -- it doesn't make it obvious to the programmer that parallel doesn't support enumerate, which is a pretty natural thing to try.  On Thursday, August 20, 2015 at 3:44:49 AM UTC-7, ele... gmail.com wrote:      ele... gmail.com    8 20 15   Certainly the error message could be more useful.  If it is possible to detect that the argument is an iterator then  parallel could do the collect itself though.      Michael Ohlrogge    Feb 13   Yes, I just lost about an hour trying to figure out what was going on here.  I didn't find it intuitive that the parallel should not work for enumeration, and the error message did little to point me in the right direction.   On Thursday, August 20, 2015 at 7:46:37 PM UTC-7, ele... gmail.com wrote: Certainly the error message could be more useful.