dplyr find running max

Asked Feb 27 '17 at 11:50

Active Apr 13 '17 at 20:13

Viewed 206 times

I'm trying to make a running maximum column by group in a dataframe. I can do this with a loop through the following but I was wondering if there was a dplyr way of doing this:

df <- data.frame(class=rep(LETTERS,each=20),
                          value=100*rpois(20*26,10))

df$runningMax <- df$value

for (i in 2:nrow(df)) {
  if (df$class[i]==df$class[i-1]) {
    # Running max of class
    df$runningMax[i] = max(df$runningMax[i],df$runningMax[i-1])
  }
}

This was my dplyr attempt:

x <- df %>%
  group_by(class) %>%
      mutate(running_max = value) %>%
      mutate(running_max = max(running_max, lag(running_max)))

Thanks for the help!

edited Apr 13 '17 at 20:13

zx8754

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asked Feb 27 '17 at 11:50

tonyk

4

Take a look at the function `cummax` – Joris Meys Feb 27 '17 at 11:51
Outside a pipeline it works but inside it gives and error, any ideas? `x % ave(df$value, df$class, FUN=cummax)` gives an error `Error in Math.data.frame(X[[i]], ...) : non-numeric variable in data frame: class ` – tonyk Feb 27 '17 at 12:03
1

`df %>% {ave(df$value, df$class, FUN=cummax)}` or `df %>% group_by(class) %>% mutate(x = cummax(value))` – Axeman Feb 27 '17 at 12:12
Perfect, thank you! – tonyk Feb 27 '17 at 12:36

dplyr find running max

0 Answers0