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MathGroup Archive 2007

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Re: Map vs. Table

  • To: mathgroup at smc.vnet.net
  • Subject: [mg75402] Re: Map vs. Table
  • From: Bill Rowe <readnewsciv at sbcglobal.net>
  • Date: Sat, 28 Apr 2007 05:59:37 -0400 (EDT)

On 4/27/07 at 5:25 AM, replicatorzed at gmail.com (zac) wrote:

>consider a set of data (y values):

>data = Table[i*j, {i, 5}, {j, 10}]

The same data can be generated more quickly with Outer. That is:

In[15]:=
Outer[Times,Range@5,Range@10]==Table[i*j,{i,5},{j,10}]

Out[15]=
True

and

In[16]:=
Timing[Do[Table[i*j,{i,5},{j,10}],{10000}];]

Out[16]=
{0.947914 Second,Null}

while

In[17]:=
Timing[Do[Outer[Times,Range@5,Range@10],{10000}];]

Out[17]=
{0.451616 Second,Null}

>I want to label each Integer with an x value:

>label := Table[{i, #} & /@ data[[i]], {i, Length[data]}]

=46or this, MapIndexed is works nicely, i.e.,

In[18]:=
Join@@MapIndexed[Outer[List,#2,#1]&,Outer[Times,Range@5,Range@
          10]]==Table[{i,#}&/@data[[i]],{i,Length[data]}]

Out[18]=
True

and

In[19]:=
Timing[Do[Join@@MapIndexed[Outer[List,#2,#1]&,data],{10000}];]

Out[19]=
{0.557445 Second,Null}

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