Counting unique / distinct values by group in a data frame

by

A data.table approach

library(data.table)
DT <- data.table(myvec)

DT[, .(number_of_distinct_orders = length(unique(order_no))), by = name]

data.table v >= 1.9.5 has a built in uniqueN function now

DT[, .(number_of_distinct_orders = uniqueN(order_no)), by = name]

More Related Contents:

  1. Reshaping data.frame from wide to long format
  2. How to sum a variable by group
  3. How do I make a list of data frames?
  4. Aggregate / summarize multiple variables per group (e.g. sum, mean)
  5. Dynamically select data frame columns using $ and a character value
  6. Sort (order) data frame rows by multiple columns
  7. Simultaneously merge multiple data.frames in a list
  8. Split data frame string column into multiple columns
  9. Filter data.frame rows by a logical condition
  10. Count number of rows within each group
  11. Quickly reading very large tables as dataframes
  12. Drop unused factor levels in a subsetted data frame
  13. Split data.frame based on levels of a factor into new data.frames
  14. Combine a list of data frames into one data frame by row
  15. Subset data frame based on number of rows per group
  16. Combine two data frames by rows (rbind) when they have different sets of columns
  17. Pass a data.frame column name to a function
  18. Drop data frame columns by name
  19. How to split a data frame?
  20. How to plot all the columns of a data frame in R
  21. Sample random rows in dataframe
  22. Extracting specific columns from a data frame
  23. Subset / filter rows in a data frame based on a condition in a column
  24. How does one reorder columns in a data frame?
  25. Convert data.frame column format from character to factor
  26. Combine two or more columns in a dataframe into a new column with a new name
  27. List distinct values in a vector in R
  28. Convert a dataframe to a vector (by rows)
  29. Dollar sign before a variable
  30. Should I use a data.frame or a matrix?

Leave a Comment