Select rows with min value by group

by

Using DWin’s solution, tapply can be avoided using ave. 

df[ df$v1 == ave(df$v1, df$f, FUN=min), ]

This gives another speed-up, as shown below. Mind you, this is also dependent on the number of levels. I give this as I notice that ave is far too often forgotten about, although it is one of the more powerful functions in R.

f <- rep(letters[1:20],10000)
v1 <- rnorm(20*10000)
v2 <- 1:(20*10000)
df <- data.frame(f,v1,v2)

> system.time(df[ df$v1 == ave(df$v1, df$f, FUN=min), ])
   user  system elapsed 
   0.05    0.00    0.05 

> system.time(df[ df$v1 %in% tapply(df$v1, df$f, min), ])
   user  system elapsed 
   0.25    0.03    0.29 

> system.time(lapply(split(df, df$f), FUN = function(x) {
+             vec <- which(x[3] == min(x[3]))
+             return(x[vec, ])
+         })
+  .... [TRUNCATED] 
   user  system elapsed 
   0.56    0.00    0.58 

> system.time(df[tapply(1:nrow(df),df$f,function(i) i[which.min(df$v1[i])]),]
+ )
   user  system elapsed 
   0.17    0.00    0.19 

> system.time( ddply(df, .var = "f", .fun = function(x) {
+     return(subset(x, v1 %in% min(v1)))
+     }
+ )
+ )
   user  system elapsed 
   0.28    0.00    0.28

More Related Contents:

  1. Deleting specific rows with a pattern[start and end indicators] from a dataframe [closed]
  2. Replace values in a dataframe based on lookup table
  3. Create a sequential number (counter) for rows within each group of a dataframe [duplicate]
  4. Sample random rows in dataframe
  5. Extracting specific columns from a data frame
  6. Subset / filter rows in a data frame based on a condition in a column
  7. Replacing character values with NA in a data frame
  8. Coerce multiple columns to factors at once
  9. Merge two data frames while keeping the original row order
  10. How to add a row to a data frame in R?
  11. Replace all particular values in a data frame
  12. Subtract a column in a dataframe from many columns in R
  13. Why am I getting X. in my column names when reading a data frame?
  14. Creating a summary statistical table from a data frame
  15. Merge rows in a dataframe where the rows are disjoint and contain NAs
  16. Add an index (numeric ID) column to large data frame [duplicate]
  17. Replace logical values (TRUE / FALSE) with numeric (1 / 0)
  18. How to delete rows where all the columns are zero
  19. Convert a dataframe to a vector (by rows)
  20. Transposing a dataframe maintaining the first column as heading
  21. Filter data frame rows based on values in vector
  22. Replace empty values with value from other column in a dataframe
  23. Split dataframe using two columns of data and apply common transformation on list of resulting dataframes
  24. Replace values in data frame based on other data frame in R
  25. Identify records in data frame A not contained in data frame B [closed]
  26. Add an image to a table-like output in R
  27. Replace value with the name of its respective column
  28. How can I merge more than 2 dataframes in R by rownames?
  29. Shifting a column down by one
  30. Identifying where value changes in R data.frame column

Leave a Comment