A variable and another variable located to its left

[Esteban Jara]

Hello. Is there a way to do an operation in Stata that performs calculations from a variable and another variable located immediately to its left, and does not depend on the name of the latter? Thank you

[Hemanshu Kumar]

Here's one way to get the name of the variable "on the left":

sysuse auto, clear

local myvar weight

unab allvars: *

local myvarpos: list posof "`myvar'" in allvars
local leftvar = word("`allvars'",`=`myvarpos'-1')

. dis "The variable left of `myvar' is `leftvar'."
The variable left of weight is trunk.

[Bjarte Aagnes]

sysuse auto , clear

local trunk trunk
local ref `trunk'
mata : st_local("left_of_`ref'", st_varname(st_varindex("`ref'")-1))

gen s = trunk + `left_of_trunk'