How to subtract a value from one column based on the value of another in R?

Question

I have a dataframe with a list of IDs of 1-2000 and each one of these IDs has multiple collections timepoints (each new collection is a new row). I have removed timepoint 1 for those with an ID of less than 1177. What I want to do now is to subtract 1 from the remaining collections for all samples that are less than 1177. For example, collection 2 will become 1 and 3 will become 2. What's the easiest way to do this?

Answer 1

I think that some code and an example df would help us to understand. However, you may do something like this

df$collection <- ifelse(df$ID > 1177, df$collection - 1, df$collection )

This only works if collection is a numerical vector. df is your dataframe