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I have 900 files that include 1,000 variables named v1 – v1000 and 1 file that includes 43 variables named v1 – v43.

My code in Stata initially opens each file using a foreach loop that imports the files while erasing the first line for each file (not shown here).

Then, I use this nested forval loop to rename variables:

forval j = 1/1000 
 local varname = strtoname(v`j'[1]) 
 rename v`j' x`varname' 

This code doesn’t work well because my last file doesn’t have the variables named v44 – v1000.

I need a code snippet that can read 1,000 variables for the first 900 files and 43 variables for the last file. I tried with c(k) (i.e. counting the number of variables in each file before looping):

forval j = 1/ `c(k)' 
 local varname = strtoname(v`j'[1]) 
 rename v`j' x`varname'

However, this doesn’t work. Any suggestions?

Using some artificially-generated datasets:

forvalues i = 1 / 10 
 clear
 set obs 5
 forvalues j = 1 / 10 
 generate v`j' = rnormal()
 
 save data`i', replace


use data10, clear
drop v5-v10
save data10, replace
clear

Here's an example:

local allfiles: dir . files "*.dta"

foreach dta in `allfiles' 
 use `dta', clear
 ds v*
 local i 0
 foreach var in `r(varlist)' 
 local ++i
 rename `var' x`i'
 
 save `dta', replace

Below you can see the results:

use data1, clear
list
 +-----------------------------------------------------------------------------------------------------------------------+
 | x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 |
 |-----------------------------------------------------------------------------------------------------------------------|
 1. | -.0658037 1.01091 .4984255 -.1489926 -.8711151 -2.013461 .2881269 .1096137 -1.400732 -.9703687 |
 2. | 2.389028 -1.537572 -.3862164 -.6072646 -2.262745 1.315605 1.686188 -.5404406 1.078409 -.117408 |
 3. | -.2777171 .6730747 -.5674241 -.578813 -.8116008 -.5623083 .7675297 -1.117687 -1.196418 .417776 |
 4. | 2.109452 -1.035937 2.063489 1.183948 -.5243855 -1.020852 -.8674071 -.3530601 -.1752301 1.556753 |
 5. | .7309901 -.6810378 -.9365283 1.818035 .0232499 2.533621 -.5896646 .5805199 .1430279 -1.926774 |
 +-----------------------------------------------------------------------------------------------------------------------+

use data10, clear
list

 +-----------------------------------------------+
 | x1 x2 x3 x4 |
 |-----------------------------------------------|
 1. | -.1145661 1.830756 1.860386 .3472159 |
 2. | 1.10806 -.5629539 1.028942 -.7665766 |
 3. | 1.269463 -1.433527 -.6405479 .8663427 |
 4. | .0158674 1.49529 2.840101 -.9815945 |
 5. | .0969952 -.0885036 -2.036327 -.2538646 |
 +-----------------------------------------------+

A very easy, not very elegant method would be to check whether the variable exists with capture:

foreach dta in `allfiles' 
 use `dta', clear
 forval j = 1/1000 
 local varname = strtoname(v`j'[1]) 
 cap confirm variable v`j'
 if (_rc == 0) rename v`j' x`varname' 
 
 save `dta', replace