A longish discussion of pros, cons, and other things can be found in this issue:
https://github.com/JuliaLang/julia/issues/249 On Thursday, May 1, 2014 11:39:14 AM UTC-5, Dominique Orban wrote: > > I would have expected b .+= 5 to change b in place, but it doesn't seem to > be the case. Isn't it counter-intuitive that it would also make a copy? > > On Thursday, May 1, 2014 6:54:10 AM UTC-7, Freddy Chua wrote: >> >> do this >> >> b = [1:5] >> f(x) = x + 5 >> map!(f, b) >> >> On Thursday, May 1, 2014 9:03:35 PM UTC+8, Kevin Squire wrote: >>> >>> b[:] = b .+ 5 >>> >>> has the behavior that you want. However, it creates a copy, does the >>> addition, then copies the result back into b. >>> >>> So, looping (aka devectorizing) would generally be faster. For simple >>> expressions like these, though, the Devectorize.jl package should allow you >>> to write >>> >>> @devec b[:] = b .+ 5 >>> >>> It then rewrites the expression as a loop. It isn't able to recognize >>> some expressions, though (especially complex ones), so YMMV. >>> >>> (Actually, it may not work with ".+", since that is a relatively new >>> change in the language. If you check and it doesn't, try submitting a >>> github issue, or just report back here.) >>> >>> Cheers! Kevin >>> >>> On Thursday, May 1, 2014, Kaj Wiik <kaj....@gmail.com> wrote: >>> >>>> OK, thanks, makes sense. But how to change the original instance, is >>>> looping the only way? >>>> >>>> On Thursday, May 1, 2014 3:12:51 PM UTC+3, Freddy Chua wrote: >>>> >>>> b = b .+ 5 >>>> >>>> creates a new instance of an array, so the original array pointed to by >>>> "b" is not changed at all. >>>> >>>> >>>> >>>> On Thursday, May 1, 2014 7:39:14 PM UTC+8, Kaj Wiik wrote: >>>> >>>> As a new user I was surprised that even if you change the value of >>>> function arguments (inside the function) the changes are not always >>>> visible >>>> outside but in some cases they are. >>>> >>>> Here's an example: >>>> >>>> function vappu!(a,b) >>>> a[3]=100 >>>> b = b .+ 5 >>>> (a,b) >>>> end >>>> >>>> c = [1:5] >>>> d = [1:5] >>>> >>>> vappu!(c,d) >>>> ([1,2,100,4,5],[6,7,8,9,10]) >>>> >>>> c >>>> 5-element Array{Int64,1}: >>>> 1 >>>> 2 >>>> 100 >>>> 4 >>>> 5 >>>> d >>>> 5-element Array{Int64,1}: >>>> 1 >>>> 2 >>>> 3 >>>> 4 >>>> 5 >>>> >>>>
