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Re: slots with 2 indexed array?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95623] Re: [mg95553] slots with 2 indexed array?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 23 Jan 2009 05:05:54 -0500 (EST)
  • Reply-to: hanlonr at cox.net

data = {{1, 2, 3}, {4, 5, 6}};

Map[g, data, {2}]

{{g[1], g[2], g[3]}, {g[4], g[5], 
     g[6]}}

data = sigs = Table[10 i + j,
    {i, 4000}, {j, 1024}];

len = Length[sigs];

f = If[# >= 2048, # - 2048, # + 2048] &;

Timing[For[i = 1, i < len + 1, i++,
  sigs[[i]] = f /@ sigs[[i]]]]

{1.3219,Null}

Timing[res = Map[f, data, {2}];]

{0.833989,Null}

Verifying that Map performs the same function

sigs == res

True


Bob Hanlon

---- "wb at wavebounce.com" <wb at wavebounce.com> wrote: 

=============
First I produce some dummy data, 4000 of what I call signals, 1024 samples each.

sigs = Table[10 i + j, {i, 4000}, {j, 1024}];
len = Length[sigs];

I'd like to modify these signals. The For statement below works. I can use a slot function on each of the sigs specified by i.

For[i = 1, i < len + 1, i++, 
  sigs[[i]] = If[# >= 2048, # - 2048, # + 2048] & /@ sigs[[i]] ]

Surely there's a way to use slots on a double indexed array but I haven't found it yet.

If I try to let # represent every entry in sigs, the If statement isn't processed:

sigs = If[# >= 2048, # - 2048, # + 2048] & /@ sigs;

I tried Which that Help says uses HoldAll but that doesn't work either; Which[] still isn't evaluated.

I tried using #2 and ## instead of # but that doesn't work.  In reading about slot functions I haven't seen any examples using multi indexed arrays.

Could someone please give me a hint on how to pull this off? -- if this can be done with slots. Thanks.




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