How to make changes in a stata string variable based on a string mata matrix of different dimensions

[Christine Alamaa]

Dear all,

I am not new to STATA but I am very new to mata. I have a problem of understanding how to use information of a matrix that I have created in mata to change some of the observations in a stata variable.

I have created a mata matrix now of dimensions 9 x 4 containing string elements that I call E. It looks as following (example):

X1/Y1	X1	Y1	Y1/X1
X2/Y2	X2	Y2	Y2/X2
X3/Y3	X3	Y3	Y3/Y3
X4/Y4	X4	Y4	Y4/X4
X5/Y5	X5	Y5	Y5/X5
X6/Y6	X6	Y6	Y6/X6
X7/Y7	X7	Y7	Y7/X7
X8/Y8	X8	Y8	Y8/X8
X9/Y9	X9	Y9	Y9/X8

Then a have a larger dataset in stata containing 916 variables and 1416 observations.
I now want to replace some of the instances in one of these variables called co_id, which is the important identifier, based on the conditions set in matrix E (in mata).
I would like to: replace co_id with the value of E[,1] (i.e col 1) if the value of co_id is found in any of the columns 2-4 in matrix E.

What I have managed to do so far is just viewing this co_id in mata by:
st_sview(Q=.,.,"co_id")

I anticipate that I should do an if else function, but I can't get my head around it.
Any help would be appreciated,

Thanks!

[German Rodriguez]

Do you really need column 4? Seems the same as column 1 except for the last entry. Assuming you already have the matrix E, you could try something like this:

mata:
    st_sview(Q=., ., "co_id")
    for(i=1; i <= 9; i++) {
        pick = select(1::length(Q), Q :== E[i,2] :| Q :== E[i,3])
        if(length(pick) < 1) continue
        Q[pick] = J(length(pick), 1, E[i,1])
    }
end

You loop over the nine possible codes (the rows), pick the indices of the data with codes in columns 2 or 3 (I assume 4 doesn't need changing), and then replace those values. The trick is to repeat the replacement code in column 1 as many times as needed.

[Christophe Kolodziejczyk]

Try to use selectindex() indstead of select() to get the indices directly