[R] N Sizes between Pairs of Columns using cor(, , , use = 'pairwise')

[Doran, Harold]

I'm trying to find an efficient way to find the N size on correlations produced when using the pairwise option in cor(). 

Here is a sample to illustrate:

### Create a sample data frame
tmp <- data.frame(v1 = rnorm(10), v2 = rnorm(10), v3 = rnorm(10), v4 = rnorm(10))

### Create some random missingness
for(i in 1:4) tmp[sample(1:10, 2, replace = FALSE), i] <- NA

### Correlate
cor(tmp, use = 'pairwise')

Now, a REALLY bad idea would be this (but conceptually it illustrates what I want)

### Identify all column pairs
pairs <- combn(4,2)

### Now, write code to loop over each pair of columns and identify where both rows are TRUE
!is.na(tmp[, pairs[,1]])

Of course doing this when the number of pairwise combinations is silly. So, hmmm, I don't see as a by-product of the cor() function N sizes, and certainly looping over pairs of columns would be doable, but not efficient, but any suggestions on this?

Thanks,
Harold