not including a "zero" in an average

[Peter Jay Salzman <p dirac org>]

hi there,

i teach a few college physics classes, and sometimes i'd like to compute
an average that doesn't include zeros.

for instance, if i want to see how my class did on a test, i'd look at
an average, but i don't want to include people who didn't show up for
the test.

is there a way to compute averages but not include zeros in the average?

thanks,
pete

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