R data.table using max in i statement

问题

This should be so simple but for some reason data.table is not doing what I expect. I want to take the max of two values in a row to determine if a row should be filtered or not. What appears to be happening is that the max() function is looking at the entire column which is not what I want. Here's the code:

> test_dt <- data.table(value1 = 1:10, value2 = 2:11, value3 = 3:12)
> test_dt[max(value1, value2, value3) < 7]
Empty data.table (0 rows) of 3 cols: value1,value2,value3

Here's what I expect:

   value1 value2 value3
1:      1      2      3
2:      2      3      4
3:      3      4      5
4:      4      5      6

What am I doing wrong here? This should be so trivial but I appear to be missing something critical.

回答1:

You want the parallel max, or pmax. See ?max for details:

test_dt[pmax(value1, value2, value3) < 7]
#    value1 value2 value3
# 1:      1      2      3
# 2:      2      3      4
# 3:      3      4      5
# 4:      4      5      6

If you really want speed, you can use pmax.int, again, see ?max for details.

来源：https://stackoverflow.com/questions/33768702/r-data-table-using-max-in-i-statement