if statement

[Belinda Foster]

Suppose I have a variable var1. What is the best/most efficient way of accessing its contents in a Mata if statement?

Something like:

..... if var1 == 23

[Christophe Kolodziejczyk]

Belinda Foster It depends. Can you be more specific about your problem?

One option is to use select or selectindex. Another is to use logical operators.

[Belinda Foster]

I am trying to generate a random variable var2 for a specific value of var1. In Stata, this is straightforward:

gen var2=rbinomial(1, 0.46) if var1=23

However, I need to do this in Mata. Any ideas?

[Christophe Kolodziejczyk]

Belinda Foster IMHO an ifelse() function is lacking in Mata. There is a mm_cond() function in the moremata package, but it is slow.

mata:

rseed(1)
x = runiform(10,1):>.5
var1 = 23*x

either

var2 = J(rows(var1),1,.)
index = selectindex(var1:==23)
var2[index] = rbinomial(rows(index),1,1,0.46)

or

var2 = rbinomial(rows(var1),1,1,0.46):*(var1:==23) // but here you evaluate more binomial variates than needed


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