CODEWITHSUNDEEP
r
Sadie Kelsey
Sadie Kelsey

Reputation: 42

calculate variance of all samples in r studio

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?

Upvotes: 0

Views: 2259

Answers (2)

Maurits Evers
Maurits Evers

Reputation: 50678

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).

Upvotes: 2

akrun
akrun

Reputation: 887223

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)

Upvotes: 0

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