Sample Mean

Calculate the mean of X in function of z

Usage

int_mean_z(z, X)

Arguments

z

A vector of 0 and 1, indicating which observations should be considered for the calculation

X

A matrix where the rows correspond to observations and the columns to variables

Value

A vector where each element is the mean for each variable

Details

This function calculates the mean of \(\boldsymbol{X}\) in function of \(\boldsymbol{z}\). If \(\boldsymbol{z}\) is a vector of 0 and 1, the mean is calculated for the \(m\) observations that are equal to 1: $$\bar{\boldsymbol{x}}(\boldsymbol{z}) = \dfrac{1}{m} \boldsymbol{X}^\top \boldsymbol{z}.$$

Examples

n <- 100
p <- 4
X <- matrix(rnorm(n * p), ncol = p)

# if we consider all the observations the result obtained is the same as colMeans()
z <- c(rep(1, n))
int_mean_z(z, X)
#> [1] -0.133657206 -0.021465456  0.005533771  0.052823144
colMeans(X)
#> [1] -0.133657206 -0.021465456  0.005533771  0.052823144