Add max value to a new column in R [duplicate]

by

We can use one of the group by functions which does allow to create a column instead of just summarise the output. The data.table option is succint as the assignment (:=) will create a new column. We convert the ‘data.frame’ to ‘data.table’, grouped by ‘a’, get the maximum value of ‘b’ (max(b)) and assign (:=) as a new column. If we need a summary, wrap it with list instead of :=.

library(data.table)
setDT(df1)[, Max:= max(b), a]

or use ave from base R. This is one of the rare base functions which will give the output as the same length of the number of rows of the original dataset. As the first argument, we use the variable to get the max of, 2nd, 3rd, etc (if any) will be the grouping column. Specify the FUN. By default, if we don’t specify any FUN, it will take the mean by group.

df1$Max <- with(df1, ave(b, a, FUN=max)

or with dplyr. The dplyr and data.table solutions are flexible in ways to get either the summary or get a new column on the original dataset. With dplyr, after we group by ‘a’, use mutate to create a new column. If, instead, we need a summarised version, the summarise function can replace the mutate (which will give similar output as aggregate).

library(dplyr)
df1 %>%
   group_by(a) %>%
   mutate(Max = max(b))
#      a     b   Max
#   (dbl) (dbl) (dbl)
#1     1     1     3
#2     1     3     3
#3     2     5     9
#4     2     9     9
#5     3     4     4

More Related Contents:

  1. Force the origin to start at 0
  2. Capitalize the first letter of both words in a two word string
  3. How to delete multiple values from a vector?
  4. Frequency count of two column in R
  5. Selecting multiple odd or even columns/rows for dataframe
  6. Format numbers with million (M) and billion (B) suffixes
  7. Rolling mean (moving average) by group/id with dplyr
  8. Generate a sequence of the last day of the month over two years
  9. How do I convert a factor into date format?
  10. Deleting reversed duplicates with R
  11. Pass a vector of variable names to arrange() in dplyr
  12. How to select a CRAN mirror in R
  13. percentage on y lab in a faceted ggplot barchart?
  14. Fill missing combinations in a dataframe
  15. Extreme numerical values in floating-point precision in R
  16. How convert decimal to POSIX time
  17. predict.lm() with an unknown factor level in test data
  18. Convert character matrix into numeric matrix
  19. Selecting only unique values from a comma separated string [duplicate]
  20. What does the diff() function in R do? [closed]
  21. Convert hours:minutes:seconds to minutes
  22. Delete entries with only one observation in a group
  23. Submit form with no submit button in rvest
  24. Using data.table i and j arguments in functions
  25. How to assign from a function with multiple outputs? [duplicate]
  26. Color points with the color as a column in ggplot2 [duplicate]
  27. How can I automatically create n lags in a timeseries?
  28. Plotting pca biplot with ggplot2
  29. Stop an R program without error
  30. How to get a barplot with several variables side by side grouped by a factor

Leave a Comment