Re: apparently I don't know how to use Map (or Apply or MapThread)

• To: mathgroup at smc.vnet.net
• Subject: [mg77361] Re: apparently I don't know how to use Map (or Apply or MapThread)
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 7 Jun 2007 03:53:34 -0400 (EDT)
• Organization: Uni Leipzig
• References: <f4676i\$1n3\$1@smc.vnet.net>

```Hi,

you mean

Table[#[[i, i]], {i, Length[#]}] &@ m

or with (Mathematica 6.0)*

Diagonal[m]

or if you whant to use Map*[]

Reap[MapIndexed[If[Equal @@ #2, Sow[#1]] &, m, {2}]][[2, 1]]

or

First /@ MapIndexed[RotateLeft[#1, #2[[1]] - 1] &, m]

or

MapIndexed[ #1[[#2[[1]]]] &, m]

or
MapIndexed[ First @ Take[#1, #2] &, m]

Regards
Jens

dbsearch04 at yahoo.com wrote:
> I started with this:
>
> m = {{0.098, 0.951, 0.954}, {0.509, 0.914, 0.487}}
>
> I tried to do this
>
> Table[#[[i, i]], {i, Length[#]}] & /@ m
>
> It does not work, but this works
>
> Diag := Function[x, Table[x[[i, i]], {i, Length[x]}]]; Diag[m]
>
> !@#\$%^&*(
>
> Can anyone tell me why? I also tried: Apply, MapThread,
> DiagonalMatrix, TakeMatrix, adding () around the pure function...
>
> I know that this is a simple problem. Would Evaluate help?
>
> TIA.
>
> Regards..
>
>

```

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