How to filter/subset a data.frame using values from one of its column [duplicate]

Question

How can I "truncate" a data.frame based on the values in a single column? For example, if I have this matrix

x <- c(5,1,3,2,4)
y <- c(1,5,3,4,2)
data <- data.frame(x,y)

and I want all data for values greater than or equal to x, how would I do that? I know that I can find the addresses of x-values using

addresses <- which(x>=2)

but I'm not sure how to use this to make a new matrix. The following do not work:

data2 <- data[x>=2]
data2 <- data[which(x>=2)]

If anyone can offer any advice, I'd really appreciate it.

Answer 1

You're not reading the error messages closely enough. Here, our error message tells you that you have not selected any columns. You've specified the condition for the rows though....

> data[which(x>=2)]
Error in `[.data.frame`(data, which(x >= 2)) : undefined columns selected

Since you want to return all columns, just put a comma in (indicating that you want all columns returned), and you should be all set.

> data[which(x>=2), ] # if x is in your workspace
  x y
1 5 1
3 3 3
4 2 4
5 4 2
> ## with(data, data[x >= 2, ] # if x is not in your workspace

---

Here's another point to note: You can make your data.frame directly like this:

data <- data.frame(x = c(5,1,3,2,4), y = c(1,5,3,4,2))

Here's why I suggest this. First, there are no unnecessary objects in your workspace. Second, you aren't fooled into thinking something is working when it isn't. You wrote that: "I know that I can find the addresses of x-values using addresses <- which(x>=2)". True, but what you perhaps didn't realize (hence this question) is that you aren't actually accessing the "x" from your data.frame but the "x" vector in your workspace.