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MathGroup Archive 1999

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RE: RE: Help to clarify 'Map', 'Apply', and ' Thread'.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15712] RE: [mg15702] RE: [mg15626] Help to clarify 'Map', 'Apply', and ' Thread'.
  • From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
  • Date: Fri, 5 Feb 1999 03:42:12 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Earlier I asked what one might do with the third argument for Thread.

***The help browser says******
Thread[f[args], h, n]
threads f over objects with head h that appear in the first n args.

Thread[f[args], h, -n]
threads over the last n args. 

Thread[f[args], h, {m, n}]
threads over arguments m through n. 

*********************

After a while I was able to come up with some meaningful examples of
what this does.  First I clear all global variables. The examples are
given below and pretty much do what the help browser says.


In[1]:=
Clear["Global`*"]


In[62]:=
lst1=f[
 g[x1,y1],
 g[x2,y2],
 g[x3,y3],a,b,c];
Thread[lst1,g,3]

Out[62]=
g[f[x1,x2,x3,a,b,c],f[y1,y2,y3,a,b,c]]


In[63]:=
lst2=f[a,b,c,
 g[x1,y1],
 g[x2,y2],
 g[x3,y3]];
Thread[lst2,g,-3]

Out[63]=
g[f[a,b,c,x1,x2,x3],f[a,b,c,y1,y2,y3]]


In[64]:=
lst3=f[a,
 g[x1,y1],
 g[x2,y2],
 g[x3,y3],c,d];
Thread[lst3,g,{2,4}]

Out[64]=
g[f[a,x1,x2,x3,c,d],f[a,y1,y2,y3,c,d]]


In[65]:=
Thread[lst3,g,{2,-3}]
Out[65]=
g[f[a,x1,x2,x3,c,d],f[a,y1,y2,y3,c,d]]

Cheers,
Ted Ersek


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