Generating values in a variable through two other variables in the dataset

[Louise Henriksen]

Hi!
I need help to create the values in a variable automatically from two other variables.

My data consists of a number of distance variables called dist_1, dist_2, dist_3 and etc which is a code for the individuals postalcode, it also consists of a variable called skolepostnr, which indicates which postalcode the school an individual attends to and postnummer, which indicates the postalcode an individual lives in. I have created a variable called dist_skole_hjem, which should be used to measure the distance between an individuals home and school, fx the individual have skolepostnr=3 and postnummer=2, so the dist_skole_hjem in this case should equal 55.

Postnummer	dist_1	dist_2	dist_3	...	skolepostnr	dist_skole_hjem
1	20,5	40,7	90		1
2	45	120	55		3
...	...	...	...		...

Since there are a lot of observations in my dataset, I would like to know if there is some way that I could generate this automatically without using the replace command like this:

replace dist_skole_hjem = 55 if postnummer == 2 & skolepostnr =="3"

So if there is some way that I could get stata to automatically fill out the dist_skole_hjem variable with the information from my dist_1, dist_2, dist_3 etc using the variables postnummer and skolepostnr and obtain the same as if I used the replace command?

Hope you can help me!

[Nick Cox]

Please read and act on FAQ Advice #12 on presenting data.

is this what you want?

clear
input float(postnummer dist_1 dist_2 dist_3 skolepostnr)
1 20.5 40.7 90 1
2   45  120 55 3
end

gen wanted = .

forval j = 1/3 {
    replace wanted = dist_`j' if skolepostnr == `j'
}

list

     +---------------------------------------------------------+
     | postnu~r   dist_1   dist_2   dist_3   skolep~r   wanted |
     |---------------------------------------------------------|
  1. |        1     20.5     40.7       90          1     20.5 |
  2. |        2       45      120       55          3       55 |
     +---------------------------------------------------------+

[Louise Henriksen]

Thank you, this was very helpful!