In R, how to sum certain rows of a data frame with certain logic?

Question

Hi experienced R users,

It\'s kind of a simple thing. I want to sum x by Group.1 depending on one controllable variable.

I\'d like

Answer 1

Not sure why Eggs are important here ;)

df1 <- data.frame(Gr=seq(4),
                  x=c(230299, 263066, 266504, 177196)
                  )

now with n=2 i.e. first two rows:

n <- 2
sum(df1[, "x"][df1[, "Gr"]<=n]) 

The expression [df1[, "Gr"]<=n] creates a logical vector to subset the elements in df1[, "x"] before summing them.

Also, it appears your Group.1 is the same as the row no. If so this may be simpler:

sum(df1[, "x"][1:n])

or to get all at once

cumsum(df1[, "x"])