Rounding/formatting a value while creating or displaying a Stata local or global macro

I love Stata’s macro functionality. It allows you to grab information from r- or e-level data after executing a Stata command then calling that back later. (Local macros are temporary, global macros are more persistent.) This is particularly useful when generating summary statistics collected in macros after the –sum– command, or displaying a subset of components from a regression, such as the beta coefficient and 95% confidence intervals, or P-values (details on how to manipulate regression function results with macros are here).

One problem in using macros is that raw r- or e-level data are really long and not amenable to output in tables for publication without formatting. I’ve hadn’t previously been able to apply formatting (eg %4.2f) while generating macros, outside of applying the “round” command. (I don’t like the round command because it’s tricky to code in a program for reasons I won’t get into.) Instead, I have applied the number formatting when displaying the macro. That creates issues when generating string output from numerical macros, since my prior strategy of applying numerical formatting (eg %4.2f) didn’t work when displaying a numerical macro in a string (i.e., embedding it within quotations). Instead, I wanted to apply the format while also generating the macro itself.

I came across this post on the Stata List by Nick Cox, which details how to do just that:

It turns out that not only can you apply formatting while generating a macro with the “: display” subcommand, you can also trim extra spaces from the generated macro at the same time. (Note that the “trim” command has been replaced by “strltrim” and a lot of other related commands that you can find in –help string functions–.) As a bonus, it turns out that you can also apply formatting (e.g., %4.2f) of a macro when displaying within a string using the “: display” subcommand strategically surrounded by opening and closing tick marks.

Here’s a demo script of what I’m getting at.

(Note: I strongly recommend against formatting/rounding/reducing precision of any macros that you are generating if you will later do math on them. Formatting during generation of macros is only useful for macros intended to be displayed later on.)

sysuse auto, clear
sum mpg
// 1. generate an unformatted macro, equals sign 
//    is required
local mpg_mean = r(mean) 
// 2. apply formatting while generating the local 
//    macro, note the colon for the macro 
//    subcommand, instead of an equals sign
local mpg_mean_fmt: display %10.2f r(mean)
// 3. here's formatting mixed with a trim command,
//    this combines an equals sign and colon. 
local mpg_mean_neat = strltrim("`: display %10.2f r(mean)'")
// Now let's call the unformatted macro from #1:
display "here it is unformatted: `mpg_mean'"
// note that it's really long after the decimal
// Let's apply formatting to #1 OUTSIDE of quotations:
display "here it is formatted " %10.2f `mpg_mean'
// ...and here's formatting to #1 WITHIN quotations:
display "here it is formatted `: display %10.2f `mpg_mean''"
// see all of the leading spaces? Using %3.2f would fix 
// that, but I wanted to show the trim function.
// here's the format applied during macro generation in 
// #2 (without a trim function):
display "here's an alt format: `mpg_mean_fmt'"
// still lots of leading spaces.
// here's trimming and formatting mixed from #3:
display "here's fmt & trim: `mpg_mean_neat'"
// Bingo!