for loop - Why is R adding an extra element to my vector? -

i have create loop takes vector z1, squares it, , creates vector z2 vectors (yes know there vectorization homework problem). i've got down except reason adds on trailing element said vector.

z1 <- c(1, 8, 19, 17, 65, 103, 48, 17, 23, 34)  # sort z1 in descending order z1 <- sort(z1, decreasing = true)  # create empty vector z2 z2 <- c()  (i in 1:10){  z2[i] <- z1[i]*z1[i]  z2 <- c(z2,z2[i]) }  print(z2) 

here's vector prints

[1] 10609  4225  2304  1156   529   361   289   289    64     1     1 

if notice has 11 elements while original z1 vector has 10. why?

first point: can operation without loop using vectorized ^ primitive function.

z1 ^ 2 # [1] 10609  4225  2304  1156   529   361   289   289    64     1 

but here's what's happening in code. need remove line

z2 <- c(z2, z2[i]) 

because on previous line have completed assignment of z2 vector, leaving final run c(z2[1:10], z2[10]). if want continue using loop, remove line.

## note difference in initializing z2 ## memory allocation more efficient building in loop z2 <- vector(typeof(z1), length(z1))  (i in seq_along(z2)) {     z2[i] <- z1[i]*z1[i] } 

and have

z2 # [1] 10609  4225  2304  1156   529   361   289   289    64     1