calculate variance of all samples in r studio

Question

I have 30 random samples taken from a data set. I need to calculate sample mean and sample variance for each sample, and arrange them in a table with 3 columns titled "sample", "mean", and "variance".

My dataset is:

lab6data <- c(2,5,4,6,7,8,4,5,9,7,3,4,7,12,4,10,9,7,8,11,8,
              6,13,9,6,7,4,5,2,3,10,13,4,12,9,6,7,3,4,2)

I made samples like:

observations <- matrix(lab6data, 30, 5)

and means for every sample separately by:

means <- rowMeans(observations)

Can you please help me to find the variance for every sample separately?

Answer 1

You can calculate the variance per row using apply :

apply(observations, 1, var)

Or use rowVars from the matrixStats package.

Note that matrixStats::rowVars will be slightly much faster (see @HenrikB's comment below) than apply(..., 1, var) , in the same way that rowMeans is faster than apply(..., 1, mean) .

Answer 2

We can use pmap to apply the function on each row of the data.frame

library(purrr)
varS <- pmap_dbl(as.data.frame(observations), ~ var(c(...)))
cbind(observations, varS)

data

observations <- matrix(lab6data, 10, 4)