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rtidyr

Select only participants with multiple rows

ID score Time
1 1000000 1
2 1000000 1
2 1000000 2
3 1000000 1
3 1000000 2
4 1000000 1
5 1000000 1
5 1000000 2

How do I subset this database to a new data base including only ID's with at least 2 follow-ups? Follow-up is resembled as "Time", whereas people with only Time 1 had one follow-up and I want to exclude them from the database. Thanks.

Solution

  • We can either use a frequency based on approach to filter the 'ID's having more than one observation after grouping by 'ID'

    library(dplyr)
df1 %>% group_by(ID) %>%
        filter(n() > 1) %>%
        ungroup()

    Or in base R - also use subset to subset the rows where it checks for 'ID's that have Time value greater than 1

    subset(df1, ID %in% ID[Time > 1])

    data

    df1 <- structure(list(ID = c(1L, 2L, 2L, 3L, 3L, 4L, 5L, 5L), 
score = c(1000000L, 1000000L, 1000000L, 1000000L, 1000000L, 1000000L, 1000000L, 1000000L), 
Time = c(1L, 1L, 2L, 1L, 2L, 1L, 1L, 2L)), 
class = "data.frame", row.names = c(NA, -8L))