如果没有满足条件的行，则返回空数据框

Question

I have a set of tables and the data in them changes. I need to remove some specific rows if there pass a condition, however in some cases, there are no rows to be removed. Instead of getting the whole data frame back I get an empty one. Here is a simplified example:

> data <- c(1,2,3,4,5,6,7)
> a <- data.frame(data)
> b <- a[-(a$data==6),]
> b
[1] 2 3 4 5 6 7
> b <- a[-(a$data==8),]
> b
numeric(0)

How should I remove the lines, so this doesn't happen?

Answer 1

It should be like this:

a[!(a$data==8),]

You may also want to use drop=FALSE to ensure the result is a data.frame :

> a[!(a$data==6),]
[1] 1 2 3 4 5 7

> a[!(a$data==6),,drop=FALSE]
  data
1    1
2    2
3    3
4    4
5    5
7    7