How to apply a function across rows in R

Problem

We'd like to apply a function across rows in R. In our example, we will add two columns calculating the minimum and the median for each row.

df <- structure(list(V1 = c(5L, 4L, 7L), V2 = c(8L, 9L, 3L), V3 = c(12L, 
5L, 9L)), .Names = c("V1", "V2", "V3"), class = "data.frame", row.names = c(NA, 
-3L))

 V1 V2 V3
1  5  8 12
2  4  9  5
3  7  3  9

Solution

dplyr

library(dplyr)
# Using the piper operator %>%
df %>% 
  rowwise() %>% 
  mutate(min= min(V1, V2, V3), median = median(c(V1, V2, V3)))
# Without the pipe operator %>%
mutate(rowwise(df), min = min(V1, V2, V3), median = median(c(V1, V2, V3)))

Source: local data frame [3 x 5]
Groups: 

     V1    V2    V3   min median
  (int) (int) (int) (int)  (int)
1     5     8    12     5      8
2     4     9     5     4      5
3     7     3     9     3      7

Base R

df$min <- apply(df, 1, min)
df$median <- apply(df[, 1:3], 1, median)

  V1 V2 V3 min median
1  5  8 12   5      8
2  4  9  5   4      5
3  7  3  9   3      7

Related posts

• Spanish version

References

• stackoverflow