using tapply to run a command, in this case calculating the variance of the variable met within each of the categories of the variable coffee consumption (3 categories)
```
tapply(coffee.exercise$met, coffee.exercise$coffee.consumption, var)
```
rowMeans, rowSums, colMeans, colSums, can do similar functions as apply. These are pretty similar to Stata's egen rowmean and rowtotal functions
Below are some examples:
```
colSums(ham, na.rm = T)
colMeans(ham, na.rm = T)
```
-
Sometimes when you are running a regression model with variables that have different lengths, r will prompt with the following error message...
-
``` library(memisc) labels(anemia$anem)<-c("not anemic"=0, "anemic"=1) #library memisc ```
