Re: How to unflatten an array ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg112845] Re: How to unflatten an array ?*From*: Ray Koopman <koopman at sfu.ca>*Date*: Sun, 3 Oct 2010 03:38:21 -0400 (EDT)*References*: <i84aed$h0e$1@smc.vnet.net> <i86uvo$hpk$1@smc.vnet.net>

On Oct 2, 2:45 am, Valeri Astanoff <astan... at gmail.com> wrote: > > Good day, > > I have to apologize for not being very clear about what I wanted. > Seems that you, Bob, were the only one to understand what I meant. > [I had to replace SplitBy with Split cause I only have version 6] > Any way I have to thank everyone who tried and help me. > Maybe this test will more explicit than my poor previous example : > [...] I think I understand now what you're doing. In[1]:= Dimensions[a1 = Table[{{x,y}, RandomInteger[99]}, {x, 0, 99}, {y, 0, 99}]] Out[1]= {100, 100, 2} In[2]:= Dimensions[a2 = Flatten /@ Flatten[a1, 1]] Out[2]= {10000, 3} In[3]:= unflatten[arr : {{_, _, _} ..}] := Module[{f}, Scan[(f[#[[1]], #[[2]]] = #[[3]]) &, arr]; Table[{{x, y}, f[x, y]}, {x, arr[[All, 1]] // Union}, {y, arr[[All, 2]] // Union}]] In[4]:= {Timing@Dimensions[a3 = unflatten[a2]], a3 == a1} Out[4]= {{1.24, {100, 100, 2}}, True} In[5]:= unflattenBob[arr : {{_, _, _} ..}] := Split[ {Most[#],Last[#]}& /@ arr, #1[[1,1]] == #2[[1,1]] &] In[6]:= {Timing@Dimensions[a3 = unflattenBob[a2]], a3 == a1} Out[6]= {{0.12, {100, 100, 2}}, True} In[7]:= unflattenRay[arr_] := Partition[Transpose@ {arr[[All,{1,2}]],arr[[All,3]]},Length@Union@arr[[All,2]]] In[8]:= {Timing@Dimensions[a3 = unflattenRay[a2]], a3 == a1} Out[8]= {{0.02, {100, 100, 2}}, True}