I have a large amount of Data where I have to count meassurments per one ID. What I already did was creating a Data Frame over all Files and I omited the NAs. This part works properly. I was wondering if the nrow-function is the right function to solve this but I figured out that this will not lead me to the target as it returns a single number as output. What I am looking for is if you have entries like that:1155 2010-05-02  2.7200    11156 2010-05-05  2.6000    31157 2010-05-08  2.6700    11158 2010-05-11  3.5700    2That I get a list:ID          Number of observations1           22           13           1
How to count observations per ID in R?
r