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MathGroup Archive 2005

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Re: Importing tab-delimited data files?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62688] Re: [mg62604] Importing tab-delimited data files?
  • From: "Dale R. Horton" <daleh at wolfram.com>
  • Date: Wed, 30 Nov 2005 22:09:02 -0500 (EST)
  • References: <200511290945.EAA08728@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On Nov 29, 2005, at 3:45 AM, AES wrote:

> I create a text file "filedata" with the following content using a  
> text
> editor, with tabs between each number or string (5 tabs per line), and
> no content -- not even a space, just successive adjacent tabs -- in  
> the
> empty slots.
>
> (The columns should line up if your reader uses monospaced type.)
>
> 11   aaa  22   bbb  33   ccc
>               22   bbb  33   ccc
>                             33   ccc
>
> Opening Mathematica and using  !!filedata  reproduces exactly same  
> thing:
>
> 11   aaa  22   bbb  33   ccc
>               22   bbb  33   ccc
>                             33   ccc
>
> Trying to follow this with
>
>    fileDataAsViewed = !!fildata
>
> or
>
>    fileDataAsViewed = %
>
> doesn't work, however.

!!file doesn't produce output, but prints the file contents as a side- 
effect. This is like doing

y = Print[x^2]

> Using the Mathematica expression
>
>    Import["datafile", "Table",
>       ConversionOptions->{"TableSeparators"->{{"\r","\n"},{"\t"}}}]
>
> gives:
>
> 11   aaa  22   bbb  33   ccc
> 22   bbb  33   ccc
> 33   ccc

The Table format assumes that multiple consecutive separators are a  
single separator. That way if you use spaces to create lined up  
columns you don't end up with a bunch of empty fields.

> Recreating the text file with a space between the tabs in the empty
> slots and applying the same  Import[ ]  expression, however, gives the
> "right" answer:
>
> 11   aaa  22   bbb  33   ccc
>               22   bbb  33   ccc
>                             33   ccc

This is because you now have a non-separator (the spaces) betweenn  
each of the separators (the tabs).

> I suppose this is not exactly unexpected.  The problem is, the app  
> that
> creates the (much larger) tab-delimited filedata text file I really  
> want
> to load into a Mathematica Table creates numerous blank cells, i.e.
> adjacent and unspaced tabs.  I guess I'll just have to go at it with a
> smart text editor and separate adjacent tabs before trying to load it.

The solution is to use the TSV (tab-separated-value) format, not the  
Table format. TSV treats each tab as new column.

Import["datafile", "TSV"]

-Dale


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