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MathGroup Archive 2004

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RE: Pipes Inside Mathematica?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45669] RE: [mg45659] Pipes Inside Mathematica?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 17 Jan 2004 02:34:39 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Harold,

There was a question similar to this just a few days ago.

{{5*Pi}, {13*E}} // IntegerPart //
  Table[0, Extract[#, 1] // Evaluate, Extract[#, 2] // Evaluate] &

If you want to use a function that requires more than one argument after //,
then use a pure function. The only extra problem in this case is that Table
has the Attribute HoldAll so we also have to Evaluate the iterators.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

From: Harold Noffke [mailto:Harold.Noffke at wpafb.af.mil]
To: mathgroup at smc.vnet.net

MathGroup:

I think Mathematica would be a better programming language if it had a
construct that allowed pipes (like Unix does).  The //-mark comes
close to facilitating this, but Mathematica needs a placeholder to
denote "result from preceding //-mark".

Here's a short example to illustrate what would be gained.

In[1]:= m = 5*Pi // IntegerPart

Out[1]= 15

In[2]:= n = 13*E // IntegerPart

Out[2]= 35

In[3]:= Table[0, {m}, {n}] // MatrixForm

Out[3]//MatrixForm=

    0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
 0   0   0

>   >       0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
:   :
:	:
:	:

    0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
 0   0   0

    >       0   0   0   0   0   0   0   0   0   0   0   0   0   0   0


What we would really like to write is the preceding computation as a
pipeline, so that it looks something like this ...

{{5*Pi},{13*E}} // IntegerPart // Table[0, Extract[<?>,1],
Extract[<?>,2]] // MatrixForm

The <?> symbol means, "I don't know what to put here" -- it's a
placeholder for whatever Mathematica wants to use as "result from
preceding //-mark".  Maybe @ would make a good placeholder here, and
what we would see on screen is ...

{{5*Pi},{13*E}} // IntegerPart // Table[0, Extract[@,1], Extract[@,2]]
// MatrixForm

I think Mathematica will be a better programming language if it adopts
some sort of pipe convention.

Harold



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