Can Stata evaluate expressions on the fly?

[Hays McLean]

I have the following little loop that works. Before creating the macro var "curvar" (which works in the next expression to add a label to a variable), I was trying to add the -word("`symbol'", `j')- to the label command [label var word("`symbol'", `j') "`I'"] and getting all kinds of syntax errors.

Is it possible in Stata to evaluate such expressions as the word() function within the code without having to create the macro var? In some coding languages there are functions such as eval(), etc. that can evaluate the expression within the code. I was wondering if such a thing exists in Stata.

*put labels on vars
local j=0
foreach i in "`lblnam'" {
local ++j
local curvar=word("`symbol'",`j')
label var `curvar' "`i'"
}

[Andrew Musau]

You can force the evaluation using macro quotes and a leading equal sign.

`=word("`symbol'", `j')'

[Nick Cox]

My guess is that the problem in #1 would be much easier to address if we had much more context and a reproducible example.

[Hays McLean]

Thanks. The nine items in "symbol" are the var names in the dataset. The 9 items in "lblnam" are the labels to be added to the cryptic var names in the same orders. The dataset contains these var names with historical price data for each. I'm just adding labels to easily explain the short, cryptic var names. Previous loops in the code create the vars and populate them with the historical data. I'm adding the labels after the dataset is created because I didn't think about it when creating the vars. Let me know if you need additional data.

I'm trying to set up the code for these products because I have more sets of products that I'm hoping to be able to use the same code with changes only in product names.

local symbol aud gbp brl cad chf eur jpy mxn nzd
local lblnam "Australian Dollar" "British Pound Sterling" "Brazilian Real" "Canadian Dollar" "Swiss Franc" "Euro" "Japanese Yen" "Mexican Peso" "New Zealand Dollar"

*put labels on vars
local j=0
foreach i in "`lblnam'" {
local ++j
local curvar=word("`symbol'",`j')
label var `curvar' "`i'"
}

[Nick Cox]

Thanks much for the detail.

There's no disgrace in just writing out 6 command lines such as

label var aud "Australian dollar"

as that is less code, much easier for most readers to grasp, and easier too for the programmer to write and maintain.

I would say the same for 60 currencies even!

Looping in your case is about as tricky as possible given a problem simple in principle. One challenge is a need to wrestle with compound double quotes too, unless I am missing something. .

I got this to work:

clear 
set obs 1 

local symbol aud gbp brl cad chf eur jpy mxn nzd
tokenize `" "Australian Dollar" "British Pound Sterling" "Brazilian Real" "Canadian Dollar" "Swiss Franc" "Euro" "Japanese Yen" "Mexican Peso" "New Zealand Dollar" "'

local j = 1 
foreach v of local symbol { 
    gen `v' = 42 
    label var `v' `"``j''"'
    local ++j 
}

describe

. describe 

Contains data
 Observations:             1                  
    Variables:             9                  
---------------------------------------------------------------------------------------
Variable      Storage   Display    Value
    name         type    format    label      Variable label
---------------------------------------------------------------------------------------
aud             float   %9.0g                 Australian Dollar
gbp             float   %9.0g                 British Pound Sterling
brl             float   %9.0g                 Brazilian Real
cad             float   %9.0g                 Canadian Dollar
chf             float   %9.0g                 Swiss Franc
eur             float   %9.0g                 Euro
jpy             float   %9.0g                 Japanese Yen
mxn             float   %9.0g                 Mexican Peso
nzd             float   %9.0g                 New Zealand Dollar
---------------------------------------------------------------------------------------
Sorted by: 
     Note: Dataset has changed since last saved.

More discussion at https://journals.sagepub.com/doi/pdf...6867X211063415