Re: Partition a list based on columns
- To: mathgroup at smc.vnet.net
- Subject: [mg119683] Re: Partition a list based on columns
- From: Ray Koopman <koopman at sfu.ca>
- Date: Fri, 17 Jun 2011 00:09:45 -0400 (EDT)
- References: <itcdai$d13$1@smc.vnet.net>
On Jun 16, 1:02 am, StatsMath <stats.ma... at gmail.com> wrote:
> [...]
>
> What would be a good way to line up elements in a list in a diagonal
> fashion, for ex: from Range[9] want to create the follwing matrix:
>
> 1 2 4
> 3 5 7
> 6 8 9
>
> Thanks in advance!
This will give an r x c matrix whose elements are
the integers 1...r*c in the positions you asked for:
m[r_,c_] := With[{d = Which[
r < c-1, Join[Range[ r ],Table[r,{c-2-r}],Range[ r ,1,-1]],
r > c-1, Join[Range[c-1],Table[c-1,{r-c}],Range[c-1,1,-1]],
True , Join[Range[c-2], Range[c-1,1,-1]]]},
Partition[FoldList[Plus,0,d],c,1] + Range@r]
m[3,5] //TableForm
1 2 4 7 10
3 5 8 11 13
6 9 12 14 15