how to filter data frame with conditions of two columns? [duplicate]

Question

I am trying to select from a data frame. The question is why I the last query below returns all 5 records not jsut the first two?

> x <- c(5,1,3,2,4)
> y <- c(1,5,3,4,2)
> data <- data.frame(x,y)
> data
  x y
1 5 1
2 1 5
3 3 3
4 2 4
5 4 2
> data[data$x > 4 || data$y > 4]
  x y
1 5 1
2 1 5
3 3 3
4 2 4
5 4 2

Answer 1

(1) For select data (subset), I highly recommend subset function from plyr package written by Hadley Wickhm, it is cleaner and easy to use:

library(plyr)
subset(data, x > 4 | y > 4)

UPDATE:

There is a newer version of plyr called dplyr (here) which is also from Hadley, but supposedly way faster and easier to use. If you have ever seen operatior like %.% or %>%, you know they are chaining the operations using dplyr.

result <- data %>%
          filter(x>4 | y>4)  #NOTE filter(condition1, condition2..) for AND operators.

(2) There indeed exist some differences between | and ||:

You can look at the help manual by doing this: ?'|'

The shorter form performs elementwise comparisons in much the same way as arithmetic operators. The longer form evaluates left to right examining only the first element of each vector. Evaluation proceeds only until the result is determined. The longer form is appropriate for programming control-flow and typically preferred in if clauses.

> c(1,1,0) | c(0,0,0)
[1]  TRUE  TRUE FALSE
> c(1,1,0) || c(0,0,0)
[1] TRUE

Per your question, what you did is basically data[TRUE], which ...will return the complete dataframe.

Answer 2

Here's something that works for me.

data[data[,1] > 4 | data[,2] > 4,1:2]

I'm not sure exactly why your method isn't working but I think it is because you're not telling it when not to print. Look at help("[").