select maximum row value by group

Question

I\'ve been trying to do this with my data by looking at other posts, but I keep getting an error. My data new looks like this:

id  year    name          


        

Answer 1

You can do this with duplicated

# your data
 df <- read.table(text="id  year    name    gdp
1   1980    Jamie   45
1   1981    Jamie   60
1   1982    Jamie   70
2   1990    Kate    40
2   1991    Kate    25
2   1992    Kate    67
3   1994    Joe     35
3   1995    Joe     78
3   1996    Joe     90" , header=TRUE)

# Sort by id and year (latest year is last for each id)
df <- df[order(df$id , df$year), ]

# Select the last row by id
df <- df[!duplicated(df$id, fromLast=TRUE), ]