# st: RE: < and > operand in recode

 From "Nick Cox" To Subject st: RE: < and > operand in recode Date Sun, 20 Aug 2006 17:51:51 +0100

```Terminology appears to be a small problem here.

I understand = to indicate equality and >, >=, < or <=
is rather surprising.

That aside, the key point is that -recode- is announced
as for recoding categorical variables, meaning
in practice categorical variables coded as
integers.

-recode- does allow many-to-one mappings, but it
really is not a good idea to use it for re-coding
a continuous variable. Even though your work-around
apparently worked for you, it is no more than
a work-around. Also, there are plenty of possible
values between 0 and 0.0001, etc., and testing
for equality and inequality with a decimal fraction
is usually problematic.

Now Stata as such doesn't really have any idea
of what a categorical variable is, and thus does
not declare your use to be an error, although
there are several good arguments for strictness
in such matters (or at least for a -force- option
which shows that you realise exactly what
you are doing).

For your coding a perfectly respectable
approach is

gen newvar = 1 if var <= 1
replace newvar = 2 if var <= 2 & missing(newvar)
replace newvar = 3 if var <= 5 & missing(newvar)
replace newvar = 4 if var <= 10 & missing(newvar)
replace newvar = 5 if var < . & missing(newvar)
replace newvar = . if var == .

That may look long-winded, but it is perfectly
explicit and easy to understand.

Another perfectly respectable approach is
make use of -inrange(,)-:

gen newvar = 1 if inrange(var,.,1)
replace newvar = 2 if inrange(var,1,2) & missing(newvar)
replace newvar = 3 if inrange(var,2,5) & missing(newvar)
replace newvar = 4 if inrange(var,5,10) & missing(newvar)
replace newvar = 5 if inrange(var,10,.) & missing(newvar)
replace newvar = . if var == .

although with -inrange()- it is not so transparent
what happens in the case of equality with either
argument. See the help for -inrange()-.

Yet another perfectably respectable approach is to
make use of -cond()-.

gen newvar = cond(var <=  1, 1,
cond(var <=  2, 2,
cond(var <=  5, 3,
cond(var <= 10, 4,
cond(var <   ., 5, .)))))

That is all one command. Careful layout and use
of a good text editor to check balanced parentheses
are recommended.

Personally, for your example problem, I like -cond()- best.

For a discursive tutorial see

SJ-5-3  pr0016  . . Depending on conditions: a tutorial on the cond() function
. . . . . . . . . . . . . . . . . . . . . . .  D. Kantor and N. J. Cox
Q3/05   SJ 5(3):413--420                                 (no commands)
tutorial on the cond() function

Nick
n.j.cox@durham.ac.uk

b. water

> Stata 8.2,
>
> i wanted to recode a variable, which consisted of continuous
> number, something to the effect of:
>
> <=1 coded 1 (<= i.e. meaning less than or equal to)
> >1 to <=2 coded 2
> >2 to <= 5 coded 3
> >5 to <=10 coded 4
> >10 coded 5
>
> when i tried to use the equality operands (i.e. < or > in my
> recode commands, it gives an error message 'unknown el <2 in
> rule') so after consulting my manual on [R] recode, i managed
> by recoding:
>
> 0.0001/1 = 1
> 1.0001/2 = 2
> .
> .
> 10/1000 = 5
> etc
>
> being careful to make sure that the parameters included all
> the values.
>
> i would appreciate if someone could confirm that equality
> sign cannot be used in recode. would appreciate it too if
> anyone can point out an alternative/better way to accomplish
> the recode.

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```