Calculator

[Kuda Makoni]

I am trying to add two means of two different variables without creating a new variable for example mean p1 + mean p2 , how do i do that?

[Joseph Coveney]

summarize p1, meanonly
scalar define mean_p1 = r(mean)
summarize p2, meanonly
display in smcl as text "Mean of p1 + mean of p2 = " as result %10.0g r(mean) + mean_p1

[ben earnhart]

Joseph Coveney was 101% correct. Proper clean syntax you can put into a .do file.

But sometimes, you just want quick and dirty. Stata can do that with display.

sum p1 p2

then
"display " (copy/paste mean1) + (copy/paste mean2)"

This approach is *not* preferred, but if you are used to documenting everything in a .do file, a little interactive command doesn't hurt, so long as it doesn't change the data

[Carole J. Wilson]

One small note about the use of scalars instead of macros: make sure that the name of the scalar is different from the variable name. Joseph Coveney chose a scalar name that was unlikely to be the same as a variable, but if there is a variable named mean_p1, the display command would have shown the value of the variable mean_p1 from the first observation instead of the desired value of the scalar. Two ways to avoid this problem:

1. use distinctive names for scalars that you would never be used for variable names
2. use the form scalar(name) to refer to scalars, as in: display scalar(mean_p1).

See Gueorgui I. Kolev, 2006. "Stata tip 31: Scalar or variable? The problem of ambiguous names". Stata Journal 6(2):279-280.

[Nick Cox]

Here's another way. The example is silly but the method is not.

sysuse auto, clear
mata : mean(st_data(. , tokens("turn trunk")))
                 1             2
    +-----------------------------+
  1 |  39.64864865   13.75675676  |
    +-----------------------------+
. mata : rowsum(mean(st_data(. , tokens("turn trunk"))))
  53.40540541

[Clyde Schechter]

Elaborating a bit on #4, another way to avoid a clash between variable names and scalar names is to use -tempname-s for scalars.

[Joseph Coveney]

I had actually initially written the post to use a tempname at first, but simplified it in order to show just the steps involved more clearly.