Svend is right, and for several variables in a row I would usually reach
for -egen-.
It is also true that for the case of two variables every possibility you
might want is achievable without recourse to -egen-.
gen sum = cond(missing(var1, var2), min(var1, var2), var1 + var2)
returns var1 if var2 is missing, and conversely, and var1 + var2
otherwise. Thus if both var1 and var2 are missing, then the result is
missing (not 0).
You could use -max()- to the same effect. Similarly, consider
gen sum = cond(missing(var1), var2,
cond(missing(var2), var1, var1 + var2))
Nick
[email protected]
Svend Juul
Satomi wrote:
..
I think egen newvar = rowtotal(var1 var2) is equivalent to replacing
missing values with 0(zero).
The SUM function in SPSS adds cases in the variable where at least one
observation is valid:
Var 1 Var2
1 4
3 5
4 5
5 8
5
.
When compute newvar= sum(var1, var2). is used, there will be 1 missing
case.
When compute newvar= var1+var2. is used, there are 2 missing cases.
=================================================================
You can gain control with -egen-'s -rowmiss()- and -rownonmiss()-
functions:
. generate plusvar = var1+var2
. egen egenvar1 = rowtotal(var1 var2)
. egen nomiss = rownonmiss(var1 var2)
. generate egenvar2 = egenvar1 if nomiss>0
. list , clean
var1 var2 plusvar egenvar1 nomiss egenvar2
1. 1 4 5 5 2 5
2. 3 5 8 8 2 8
3. 4 5 9 9 2 9
4. 5 8 13 13 2 13
5. . 5 . 5 1 5
6. . . . 0 0 .
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