[Tutor] Converting a string into dictionary references

[Gerhardus Geldenhuis]

Thanks!
That does look helpfull, I will give it a go and see if I can get an
alternative version working.

Regards

On 23 April 2012 17:40, Don Jennings <dfjennings at gmail.com> wrote:

> Remember, the keys for the dictionary in your example are simply strings.
> It just so happens that those strings are in another file. Read the file
> which contains the specified columns and split on the comma into variable
> names for your output:
>
>
> with open(spec_file, 'r') as f:
>    outcol1, outcol2, outcol3 = f.readline().split(',')
>
> # use variable names to access dictionary
> print row[outcol1] + ',' + row[outcol2] + ',' + row[outcol3]
>
>
> Now, if you are unsure how many columns will be in the file with specified
> columns, that changes things slightly:
>
>
> # get a list of the requested columns
> outcols = []
> with open(spec_file, 'r') as f:
>    line = f.readline()
>    outcols.extend(line.split(','))
>
> # later, use that list to do something with the output (I assume strings
> for your data here)
> print ','.join([row[outcol] for outcol in outcols])
>
> Helpful?
>
> Take care,
> Don
>
>
> > Not quite,
> >
> > I have csvfile1:
> > column1, column2, column3, ... column200
> >
> > That is my raw data but I want to use only 5 columns for example in a
> > specific application.
> > I thus want a file with the following:
> > column33,column1,column5
> >
> > I then want to read the original csv file and write a new csv file with
> the
> > requested columns only.
> >
> > Does that make more sense?
> >
> > Regards
> >
> > On 23 April 2012 14:41, Joel Goldstick <joel.goldstick at gmail.com> wrote:
> >
> >> On Mon, Apr 23, 2012 at 8:56 AM, Gerhardus Geldenhuis
> >> <gerhardus.geldenhuis at gmail.com> wrote:
> >>> Hi
> >>> Appologies about the subject I could not think of a better description.
> >>>
> >>> I have this very simple function:
> >>>
> >>> def readcsvfile(filename):
> >>>  f = open(filename, 'ro')
> >>>  csvdata = csv.DictReader(f)
> >>>  for row in csvdata:
> >>>    print row["column3"]+','+row["column1"]
> >>>
> >>> I have another inputfile that will be comma separated list of values.
> >>> Eg:
> >>> column3,column4,column10
> >>>
> >>> The idea is that I use this inputfile to tranform the original csv
> file.
> >> I
> >>> thus want a new file with only the specified columns. I am sure there
> is
> >> an
> >>> elegant way of doing this but I am not sure how to convert my print
> >>> statement into something more dynamic. Any pointers would be
> appreciated.
> >>>
> >>> Regards
> >>>
> >>> --
> >>> Gerhardus Geldenhuis
> >>>
> >>> _______________________________________________
> >>> Tutor maillist  -  Tutor at python.org
> >>> To unsubscribe or change subscription options:
> >>> http://mail.python.org/mailman/listinfo/tutor
> >>>
> >>
> >> So you want to take 'column1' and get back 1?, 'column10' and get back
> 10?
> >>
> >> s = 'column1'
> >> i = int(s[6:])
> >>
> >> This will only work if your strings all start with the text 'column'
> >>
> >> --
> >> Joel Goldstick
> >>
> >
> >
> >
> > --
> > Gerhardus Geldenhuis
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>


-- 
Gerhardus Geldenhuis
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