Nick, Scott, Ronan,
These are good tips. The " " was really straightforward, strange that
that didn't occur to me. The encode and inlist syntax will be very
useful for what I'm doing.
Tewodaj
_______________________________________________________________________
_
Message: 10
Date: Wed, 10 Nov 2004 16:45:28 +0000
From: Ron�n Conroy <[email protected]>
Subject: Re: st: RE: Dealing with string variables
Nick Cox wrote:
>drop if grain == "wheat"
>
>value labels for string variables:
>not allowed
>
>what you want is better done by
>
>gen Crop = "crop" if inlist(crop, "wheat", "barley")
>replace Crop = "root" if inlist
(crop, "potato", "cassava", "yams", "beet")
>...
>
>
>
using -encode-
. label define crop 1 "wheat" 2 "barley" 3 "root", modify
. encode crop, gen(Crop) label(crop)
. replace Crop=3 if inlist(crop, "potato", "cassava", "yams", "beet")
. replace Crop=. if Crop > 3
Logic:
1. start by defining a label that will assign numeric codes to the
strings in a logical order. In a do-file, always follow this by -
modify-
in case the label is already defined in some way.
2. use -encode- to generate a new variable, using the predefined
mappings. Strings that are not found in the predefined value label
will
be added to the value label, using unassigned numbers. For this
reason,
nothing will be assigned the number 3 because we reserved this for a
new
category, "root".
3. Nick's nice piece of code that checks for root crops. You could use
the -index- function for a single string, but -inlist- is more
general.
-index- has some neat uses; this isn't one of them.
4. Any remaining values are ones that we don't need (strings like "not
applicable" or other crops that don't interest us). These will have
been
assigned value labels and numeric codes that can be inspected easily
by
typing
. lab list crop
~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~
Tewodaj Mogues
Dept. of Agricultural and Applied Economics
University of Wisconsin - Madison
427 Lorch St. #317, Taylor Hall
Madison, WI 53706
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