swolf - 5 months ago 21

R Question

I just can't get my head around this quite simple task and reading up on related problems on this site did not help.

I created a minimal example:

`a <- data.table(n = c("case1", "case2", "case3"), x = c(0,2,5), y = c(1,1,4), z = c(1,1,0))`

cols <- c("x", "y", "z")

a

n x y z

1: case1 0 1 1

2: case2 2 1 1

3: case3 5 4 0

All I want to do is to select all rows from

`a`

`cols`

So what I want to get in this case is:

`n x y z`

2: case2 2 1 1

I used apply in combination with

`all()`

`cols`

Answer

We can use `Reduce`

with `.SDcols`

. Specify the columns of interest in `.SDcols`

, loop through the Subset of Data.table (`.SD`

) check whether it is equal 0, get the sum of each row with `Reduce`

, negate (`!`

) to get a logical vector which returns TRUE when there are no 0 elements and use that to subset the rows of 'a'

```
a[a[, !Reduce(`+`, lapply(.SD, `<=`, 0)),.SDcols = cols]]
# n x y z
#1: case2 2 1 1
```

Or as @Frank mentioned in the comments, `pmin`

can be used as well

```
a[a[, do.call(pmin, .SD), .SDcols = cols]>0]
```