How to calculate Mean of median-centered z-score

Hi there,

How is it possible to calculate the Mean of the median-centered z-score? Taking the below script as an example of a data frame. I need to develop a score for each subject. (My dataset is different this is just an example)

Thank you!

Imran

student_id <- seq(1,10)

math <- c(502,600,412,358,495,512,410,625,573,522)

science <- c(95,99,80,82,75,85,80,95,89,86)

english <- c(25,22,18,15,20,28,15,30,27,18)

df_student <- data.frame(student_id,math,science,english)

View(df_student)

z <- scale(df_student[,2:4],center=TRUE,scale=TRUE)

View(z)