Imagine I have measurements of 5 participants, performed on different days. The number of measurements differs between the participants. I would like to know at how many days measurements were performed for every participant
Let's say I have the following data frame (see image):
view(df)
Id Date
1 1-2-2019
1 2-2-2019
2 5-2-2019
2 5-2-2019
3 8-2-2019
4 7-2-2019
5 9-2-2019
5 1-3-2019
5 11-4-2019
I am looking for the following result:
Id Days
1 2
2 1
3 1
4 1
5 3
I have tried something like length(unique(df$date), by="Id")
