Why the unab result would not be displayed?

[Zoey Gu]

Hi all statalisters,

I'm confused by the unab function when the result cannot be displayed. I guess it is because the unab function doesn't work as command. Here's the screenshot

After I input display, it doesn't work. I wonder if the unab function doesn't work out or if I need to reset something.

Thank you !!

[Clyde Schechter]

You see that "end of do file" after the -unab- command? That's the reason the display command shows nothing. -unab- creates a local macro, and local macros go out of scope (disappear) at the end of the program or do-file that creates them. This is a common error people make when using Stata, trying to run code that contains local macros one line at a time. That never works. When local macros are involved, the entire code from the creation of the local macro through the last reference to it must be run all together without interruption.

Here's a short do-file:

clear*

sysuse auto

unab X: price mpg weight

display "`X'"

When I run it all at once from beginning to end you get the result of -unab- displayed:

. do "C:\Users\clyde\AppData\Local\Temp\STD6158_000000.tmp"

. clear*

.
. sysuse auto
(1978 automobile data)

.
. unab X: price mpg weight

.
. display "`X'"
price mpg weight

.
end of do-file

But if I run it line by line:

. do "C:\Users\clyde\AppData\Local\Temp\STD6158_000000.tmp"

. clear*

.
end of do-file

. do "C:\Users\clyde\AppData\Local\Temp\STD6158_000000.tmp"

. sysuse auto
(1978 automobile data)

.
end of do-file

. do "C:\Users\clyde\AppData\Local\Temp\STD6158_000000.tmp"

. unab X: price mpg weight

.
end of do-file

. do "C:\Users\clyde\AppData\Local\Temp\STD6158_000000.tmp"

. display "`X'"


.
end of do-file

local macro X is destroyed immediately after it is created, and the subsequent attempt to display it produces no output.

[Zoey Gu]

It worked so perfectly and make all sense to me! @Clyde Schechter Thank you so much for immediate response!!
Sorry I have an additional question: the local macro runs at once and cannot be runned line by line? What about the global macro?
Thank you!

[Nick Cox]

Global macros are visible everywhere once they have been defined. That's not a good reason to use them. In any case unab doesn't produce a global macro as result, even optionally. You would need to copy what it creates to a global macro, and that's not recommended.

More on this problem -- which is one of understanding, not one of use -- at https://journals.sagepub.com/doi/pdf...36867X20931028

Note that unab is a command, not a function. In Stata, commands and functions are disjoint, so that function is not another name for command.

[Zoey Gu]

@Nick Cox make sense！ Now I understand the difference and how macro works, thank you !