results of a selectindex: is it a pointer or scalar

[Saeed Sardar]

I am trying to locate an element of a matrix and extract its row index with selectindex function. However, when the selectindex is empty, I cannot figure out how to evaluate that condition. See the following example:

mata
y=2004::2010
y[3,1]=.
y
row=selectindex(y[.,1]:==2007)
row!=0
row=selectindex(y[.,1]:==2006)
// now row is niether zero or empty and I cannot find a way to evaluate if condition based on the value of row. see
row!=0
row!=.
row!=""

my question is how can I write and IF condition that see whether row is empty or not.

[Christophe Kolodziejczyk]

It returns an empty matrix if no rows/columns satisfy the condition. Test whether the number of rows or columns is different from 0 (in your case you should test the number of rows)

if (rows(row)!=0)

[Saeed Sardar]

Fantastic, thank you.