Re: st: saving space while recoding

[Eric Booth <ebooth@ppri.tamu.edu>]

<>


There are a couple of possibilities here.   First, you can get rid of the 3 -replace- statements with one -recode- statement that does the same thing, e.g., 

******!
recode polyclornew (min/44 = -1)  (45=0)  (46/max = 1) (.=.)
******!

but this doesn't make managing your long list of recode conditions much easier.  Also,  a warning: note that the -replace- codes in your example will not recode any values between 44 and 45 (such as 44.5)  nor values between 45 & 46.  Given that a lot of the values in the list your provided aren't integers, this might be a concern. 

In terms of making your code shorter you might consider using the -cond()- function.  For example, 
**********************!
sysuse auto, clear
keep price
qui g i = cond(price==4099, 0, cond(missing(price), ., (cond(price<4099, -1, 1))))
sort price
**********************!
will recode price around the 4,099 threshold.  
A brief explanation of what this code is doing is probably helpful here:    if price is == 4099 it will recode i to 0.   If not, it will evaluate the  last "cond(missing(price), ., (cond(price<4099, -1, 1)) " part.    Within this last part it will recode i to -1 if price is less than 4099 and i to 1 if price is greater than or equal to 4099 (but it has already recoded to 0 if price is equal to 4099, so it will just recode to 1 if price is greater than 4099 in this case) .  See -help cond- for more.

To make this work with a long list of conditions like the ones you have provided, you could break the list up into macros &/or  use -tokenize- to loop over the pairs of items in your list.  Here are two examples using the -auto.dta- again:


**********************!
//EXAMPLE 1//
    /*
This example uses the list if it is formatted as you presented it in your posting--it will make the changes to items 1 (mpg) and 2(23) in the list and then move on the items 3 and 4 in the list and so on to the end
    */

sysuse auto, clear
local list  mpg 23  rep78 3 turn 17 weight 2930 length 196
**
token `"`list'"'
di `"`list'"'
	while "`1'" != "" {
	 di "recode `1' for value `2'"
	  g i`1' = cond(`1'==`2', 0, cond(missing(`1'), ., (cond(`1'<`2', -1, 1))))
	  mac shift 2    //this part increases the macro `1' by 2 to `3'
	}
sort mpg
order *mpg
**********************!

Alternatively, if your list were organized down a column in a spreadsheet or something, you could add -local- and a macname to each pair of items to be used for the recodes and loop over each condition.  

**********************!
//EXAMPLE 2//
sysuse auto, clear

**items in your list:
local one  mpg 23
local two  rep78 3
local three turn 17
local four weight 2930
local five length 196

foreach x in one two three four five {
	token ``x''
	di "``x''"
	di "recode `1' for value `2'"
	  g i`1' = cond(`1'==`2', 0, cond(missing(`1'), ., (cond(`1'<`2', -1, 1))))
}
sort mpg
order *mpg
**********************!

~ Eric
__
Eric A. Booth
Public Policy Research Institute
Texas A&M University
ebooth@ppri.tamu.edu
Office: +979.845.6754





On Jul 24, 2010, at 4:22 PM, sarah plank wrote:

> I need to create a recode but save some space in my code.   I have
> lots of recodes where I am given the variable to recode and the cutoff
> point over which to recode the variables.  So, given my list of
> "polyclor 23.4    polyclor2  33.3  pavol 45  genpt  1.11  gnpt  1  on
> 0  offon 0  offon2 1  got5  66  {+ 670 more items}"  I need to recode
> them all by their cutoff in the list, so
> 
> clonevar polyclor2 = polyclornew
> replace polyclornew = -1 if polychlornew<44
> replace polyclornew = 0 if polyclornew==45
> replace polyclornew = 1 if polyclornew>46 & polyclornew!=.
> tab polyclornew
> 
> but this is so exhausting for so many values and so long in the
> do-code.  How can I make this in less space ?
> 
> *
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> *   http://www.stata.com/help.cgi?search
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> *   http://www.ats.ucla.edu/stat/stata/





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