Finding maximum value for column among a subset of a data frame

Question

Given a data frame `df` with columns `d`, `c`, `v`. How do I find the value of `d` for the maximum value of `v` among the subset of records where `c == "foo"`? I tried this: ``` df[df$v==max(df$v) & df$c == "foo","d"] ``` But I got: ``` character(0) ```

Accepted Answer

Yo can do as follows:

```
with(df, d[v== max(v[c=="foo"])])
```

EDITED: If you want to get the value of `d` for all the levels of `c`:

```
library(plyr)
ddply(df, "c", subset, v==max(v))
```

Finding maximum value for column among a subset of a data frame

Solution

Problem