Merge nearest date, and related variables from a another dataframe by group

Question

I have two dataframes each with multiple rows per ID. I need to return the closest date and related data from the second dataframe based on the ID and date of the first data

Answer 1

We can also do this by one-liner with dplyr.

library(dplyr)

left_join(df1, df2, by = "ID") %>%
  mutate(dateDiff = abs(dateTarget.x - dateTarget.y)) %>%
  group_by(ID, dateTarget.x) %>%
  filter(dateDiff == min(dateDiff))