Question

Possible Duplicate:
Extracting indices for data frame rows that have MAX value for named field

hello,

I have a data frame like this :

   A1 A3    d
1   a pr    5
2   a be    0
3   a cd    8
4   a dy    0
5   b pr    3
6   b be    4
7   b cd    9

etc...

I want to test each row, and get the unique rows based on A1 and have max value of d

the output should be like this

A1 A3 d
a  cd 8
b  cd 9

etc..

The data frame is bigger , but that’s an example.

Can this be done with R? without looping and long stuff??

thanks

Answer 1

The easiest way to do it is to sort the d column, and them remove duplicates in the A1 column:

df2 <- df[order(df$d,decreasing=T),]
df2[!duplicated(df2$A1),]

This does assume that there is a single unique maximum, you would lose some results if there were more than 1.