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Newsgroups: comp.lang.python
Date: Wed, 2 Jan 2013 18:41:46 -0800 (PST)
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Subject: Re: avoding the accumulation of array when using loop.
From: Isaac Won <winefrog@gmail.com>
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On Wednesday, January 2, 2013 5:54:18 PM UTC-6, Dave Angel wrote:
> On 01/02/2013 05:21 PM, Isaac Won wrote:
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> > Hi all,
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> >
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> > Thanks to Hans, I have had a good progress on my problem.=20
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> >
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> > Followings are Hans's Idea:
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> >
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> > import numpy as np=20
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> >
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> > b =3D []=20
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> > c =3D 4=20
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> > f =3D open("text.file", "r")=20
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> >
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> > while c < 10:=20
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> >         c =3D c + 1=20
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> >
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> >
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> >         f.seek(0,0)=20
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> >
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> >         for  columns in ( raw.strip().split() for raw in f ):=20
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> >                 b.append(columns[c])=20
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> >
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> >         y =3D np.array(b, float)=20
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> >         print c, y=20
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> >
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> >
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> > It's a bit inefficient to read the same file several times.=20
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> Don't bet on it.  The OS and the libraries and Python each do some
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> buffering, so it might be nearly as fast to just reread if it's a small
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> file.  And if it's a huge one, the list would be even bigger.  So the
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> only sizes where the second approach is likely better is the mid-size fil=
e.
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> > You might consider reading it just once.  For example:=20
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> >
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> >
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> > import numpy as np=20
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> >
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> > b =3D []=20
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> >
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> >
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> >
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> > f =3D open("text.file", "r")=20
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> >
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> > data =3D [ line.strip().split() for line in f ]=20
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> > f.close()=20
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> >
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> > for c in xrange(5, 11):=20
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> >         for row in data:=20
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> >                 b.append(row[c])=20
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> >
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> >
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> >         y =3D np.array(b, float)=20
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> >         print c, y=20
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> > -----------------------------------------------------------------------=
--------
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> >
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> > It is a great idea, but I found some problems. I want each individual a=
rray of y. However, these two codes prodce accumulated array such as [1,2,3=
], [1,2,3,4,5,6], [1,2,3,4,5,6,7,8,9] and so on. I have tried to initialize=
 for loop for each time to produce array. This effort has not been very suc=
cessful.
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> > Do you guys have any idea? I will really appreciate ant help and idea.
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> Your description is very confusing.  But i don't see why you just don't
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> just set b=3D[] inside the outer loop, rather than doing it at the begin
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> of the program.
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> for c in xrange(5, 11):=20
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>         b =3D []
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>         for row in data:=20
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>                 b.append(row[c])=20
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> --=20
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> DaveA

Hi Dave,

I really appreciate your advice. It was really helpful.

Isaac