Using apply

  • Applies a function to the rows or columns of a dataframe/matrix
  • apply(X, MARGIN, FUN)
  • X is the data
  • MARGIN is whether we're doing rows or columns (1 or 2)
  • FUN is the function

If you're anything like me, you will never get MARGIN correct on the first try. Simply trying both is fine, but a useful way to think about it:

If we have a 10 x 5 dataframe d1, (10 rows with 5 columns), MARGIN controls which dimension stays the same:

  • apply(d1, 1, mean) will return a 10 x 1 output, the mean for each row
  • apply(d1, 2, mean) will return a 1 x 5 output, the mean for each column

Using apply

  • Applies a function to the rows or columns of a dataframe/matrix
  • apply(X, MARGIN, FUN)
  • X is the data
  • MARGIN is whether we're doing rows or columns (1 or 2)
  • FUN is the function

If you're anything like me, you will never get MARGIN correct on the first try. Simply trying both is fine, but a useful way to think about it:

If we have a 10 x 5 dataframe d1, (10 rows with 5 columns), MARGIN controls which dimension stays the same:

  • apply(d1, 1, mean) will return a 10 x 1 output, the mean for each row
  • apply(d1, 2, mean) will return a 1 x 5 output, the mean for each column