Create a List from a Vector

[Carole J. Wilson]

Is there an efficient way of moving a column or row vector with strings into a list so as to use with macrolists in Stata? Since the vectors can be thousands of values, I would rather not loop over each element.

I have a two string matrices (vectors, actually) in Mata containing values of a numeric variable, including extended missing values stored as .a .b. etc. I can move these to Stata matrices.

I ultimately would like a macro list with the elements of A that are not in B. Were they in list form, I could easily get this with : list A - B.

(A couple of almost solutions in Mata: this post gives a way to get the common elements from real matrices; and -indexnot- only works 1 character elements.) I'm a Mata newbie, so a Stata solution would be easier for me to understand, but I'm open to Mata if there is an efficient solution.

mata: A=(1, 2, 3, 10, .a, .b, .c)
mata: B=(1, 2, .a)
mata: st_matrix("A", A)
mata: st_matrix("B", B)
mat list A
mat list B

Thanks,
Carole

[daniel klein]

If there are no embedded spaces in your Mata vector, you can get it directly into a Stata local. Using your example

mata: A=(1, 2, 3, 10, .a, .b, .c)
mata: B=(1, 2, .a)

mata : st_local("A", invtokens(strofreal(A)))
mata : st_local("B", invtokens(strofreal(B)))

local A_not_in_B : list A - B
display "`A_not_in_B'"

Best
Daniel

[Nick Cox]

I don't know about efficient: in terms of speed; storage; something else? Does efficient mean elegant?

Any way, here is one way to do it. It could no doubt be made shorter at the cost of a little clarity. I haven't tried much bigger examples.

 mata
 A=(1, 2, 3, 10, .a, .b, .c)
 B=(1, 2, .a)
 st_local("Alist", invtokens(strofreal(A)))
 st_local("Blist", invtokens(strofreal(B)))
 end
 local diff : list Alist - Blist
 mac li

[Carole J. Wilson]

Thank you Daniel & Nick!
Any suggestions on a good Mata book? I love the Stata manuals--they are extremely clear, but I have a very difficult time understanding the Mata manual. The start of each entry is a complete mystery to me. I re-read the beginning hoping that I overlooked something, but I need a primer on how to read the manual!

[Nick Cox]

There is no book dedicated to Mata. Many people wish that weren't so.

[daniel klein]

Some good resources are mentioned here.

Best
Daniel

[Carole J. Wilson]

Much appreciated, Daniel!