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Re: st: saving space while recoding


From   Jeph Herrin <stata@spandrel.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: saving space while recoding
Date   Mon, 26 Jul 2010 08:07:03 -0400

You find -irecode- useful:

  gen var = irecode(newvar2,22,25,.)-1


hth,
Jeph

On 7/25/2010 10:14 PM, sarah plank wrote:
Now I have a second list given me where there are some ranges instead
of single cutoff points, so for list  "newvar2 22 25  newvar3  33.5
26  newvar9  55.5  100 "  I need to recode values less than first
range point to -1, values between range to zero, and points above the
second range point to 1.  With the replace command, I can do it:
generate var = -1 if newvar2<=22
replace var = 0 if newvar2>=22&  newvar2<=25
replace var = 1 if newvar2>= 25&  newvar2!=.

and I tried to paste this into the code I got earlier but it doesnt work.
gen var = cond(22<=newvar2<=25, 0, cond(missing(newvar2), .,
(cond(newvar2<22, -1, 1))

This gives me all zeros !  How can I edit this code to work with my
new list and make this work in a loop to save space ?





On Sat, Jul 24, 2010 at 5:58 PM, sarah plank<sarahkplank@gmail.com>  wrote:
Oh my gosh, how great!   I copied and pasted my list into the first
example and it is working, I am running it now but I hope it doesnot
break because I dont understand it enough to make changes.  Thanks.

On Sat, Jul 24, 2010 at 4:35 PM, Eric Booth<ebooth@ppri.tamu.edu>  wrote:
<>


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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