Hi Henning,
Henning Wildhagen wrote:
Given a dataframe of three columns, where col1 is of type factor, col 2 and
col3 are numeric and pairs of observations i would like to perform a paired
t-test for each level of col1.
I would like to avoid specifying the levels of col1 manually because it
seems to me as being stupid, however, i did not figure out how to tell it R
in an function. I tried with tapply, but it did not work.
That's what 'tapply' is meant for. Try this:
tapply( 1:nrow(df), df$col1, function(r)
t.test( df$col2[r], df$col3[r], paired=TRUE ) )
Here, tapply calls the fucntion in the second line for each level of
col1, always passing the row indices of the rows with this level as
parameter 'r'.
HTH
Simon
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