Remove blank lines from string colvector

[Archibald Dunlop]

If I have a string colvector in Mata, how can I create a new string colvector that removes rows with empty lines?

[William Lisowski]

: a = ("dog" \ "" \ "cat")

: a
         1
    +-------+
  1 |  dog  |
  2 |       |
  3 |  cat  |
    +-------+

: b = a:!=""

: b
       1
    +-----+
  1 |  1  |
  2 |  0  |
  3 |  1  |
    +-----+

: select(a,b)
         1
    +-------+
  1 |  dog  |
  2 |  cat  |
    +-------+

:

[Archibald Dunlop]

Thank you! I ended up using

b = select(a, strlen(a))

. Is this directly equivalent?

[William Lisowski]

Yes, for what you are doing. Post #2 demonstrates technique that can be generalized to other selections defined with a logical expression.

[daniel klein]

Thank you! I ended up using

b = select(a, strlen(a))

. Is this directly equivalent?

At some level, it is probably a fraction of a (milli-)second slower to get the length of (all) strings (in the vector) than comparing against null string.