将数据框中的所有行从第一个匹配项拖放到最后一行

Question

I'd like to drop all the rows in a data frame from the first row that matches a condition through to the last row.

This is what I've got in base R, to find the row where disp is 400, and drop that row and all the rows from that row to the last row:

mtcars[-c(which(mtcars$disp == 400):nrow(mtcars)), ]

How can I do this with dplyr and/or data.table?

Answer 1

In dplyr , you can use cumsum inside filter . Once you hit the first 400, cumsum increases to one.

mtcars%>%
  filter(cumsum(disp==400)<1)

Here's the equivalent in data.table :

mtcars <- as.data.table(mtcars)
mtcars[cumsum(disp==400)<1]