On Monday, December 31, 2012 6:59:34 AM UTC-6, Hans Mulder wrote:
> On 31/12/12 11:02:56, Isaac Won wrote:
>
> > Hi all,
>
> > I am a very novice for Python. Currently, I am trying to read continuous
>
> > columns repeatedly in the form of array.
>
> > my code is like below:
>
> >
>
> > import numpy as np
>
> >
>
> > b = []
>
> > c = 4
>
> > f = open("text.file", "r")
>
> >
>
> > while c < 10:
>
> > c = c + 1
>
> >
>
> > for columns in ( raw.strip().split() for raw in f ):
>
> > b.append(columns[c])
>
> >
>
> > y = np.array(b, float)
>
> > print c, y
>
> >
>
> >
>
> > I thought that can get the arrays of the columns[5] to [10], but I only
>
> > could get repetition of same arrays of columns[5].
>
> >
>
> > The result was something like:
>
> >
>
> > 5 [1 2 3 4 ......, 10 9 8]
>
> > 6 [1 2 3 4 ......, 10 9 8]
>
> > 7 [1 2 3 4 ......, 10 9 8]
>
> > 8 [1 2 3 4 ......, 10 9 8]
>
> > 9 [1 2 3 4 ......, 10 9 8]
>
> > 10 [1 2 3 4 ......, 10 9 8]
>
> >
>
> >
>
> > What I can't understand is that even though c increased incrementally upto
> > 10,
>
> > y arrays stay same.
>
> >
>
> > Would someone help me to understand this problem more?
>
>
>
> That's because the inner loop read from a file until his reaches
>
> the end of the file. Since you're not resetting the file pointer,
>
> during the second and later runs of the outer loop, the inner loop
>
> starts at the end of the file and terminates without any action.
>
>
>
> You'd get more interesting results if you rewind the file:
>
>
>
> import numpy as np
>
>
>
> b = []
>
> c = 4
>
> f = open("text.file", "r")
>
>
>
> while c < 10:
>
> c = c + 1
>
>
>
> f.seek(0,0)
>
> for columns in ( raw.strip().split() for raw in f ):
>
> b.append(columns[c])
>
>
>
> y = np.array(b, float)
>
> print c, y
>
>
>
> It's a bit inefficient to read the same file several times.
>
> You might consider reading it just once. For example:
>
>
>
> import numpy as np
>
>
>
> b = []
>
>
>
> f = open("text.file", "r")
>
> data = [ line.strip().split() for line in f ]
>
> f.close()
>
>
>
> for c in xrange(5, 11):
>
> for row in data:
>
> b.append(row[c])
>
>
>
> y = np.array(b, float)
>
> print c, y
>
>
>
>
>
> Hope this helps,
>
>
>
> -- HansM
Hi Hans,
I appreciate your advice and kind tips.
The both codes which you gave seem pretty interesting.
Both look working for incrementing inner loop number, but the results of y are
added repeatedly such as [1,2,3],[1,2,3,4,5,6], [1,2,3,4,5,6,7,8,9]. Anyhow,
really thank you for your help and I will look at this problem more in detail.
Isaac
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