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rdataframemaxunique

Max value of a column based on every unique value of another column (Dataframe)

I'm trying to get the max value of y per unique value of id.

id <- c("1", "1", "1", "2", "2", "2")
y <- c("2.43", "2.11", "2.31", "3.11", "2.12", "2.10")
output <- c("2.43", "2.43", "2.43", "3.11", "3.11", "3.11")

df <- data.frame(id, y, output)

  id    y output
1  1 2.43   2.43
2  1 2.11   2.43
3  1 2.31   2.43
4  2 3.11   3.11
5  2 2.12   3.11
6  2 2.10   3.11

Any help would be much appreciated!!

Solution

  • We can use group_by 'id'

    library(dplyr)
df %>%
    type.convert(as.is = TRUE) %>%   
    group_by(id) %>% 
    mutate(output = max(y))

    Or with ave from base R

    df <- type.convert(df, as.is = TRUE)
df$output <- with(df, ave(y, id, FUN = max))