r - colMeans with condition based on one of the column -


newbie here.

so have matrix dimension of 3*24. trying find mean of 3rd column if value of 2nd column in greater/lower x. values numeric.

what have been trying follow:

over40<-trainexer11$age>=40 below40<-trainexer11$age<40

the idea create logical variable each age group

colmeans(trainexer11, below40=true)

then find mean of both variable if fulfils previous logical.

the code returned error (obviously) since not familiar r yet, don't know how 1 should proceed

we can use aggregate

aggregate(trainexer11~ agegrp, transform(df1, agegrp = age >=40), fun = mean)

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