Exercise Chapter 1

library(magrittr)

# ======================
# BÀI 1: Mean of Positive Values
# ======================

bai1_result <- rnorm(1000) %>%
  replace(. < 0, NA) %>%
  mean(na.rm = TRUE)

bai1_result

## [1] 0.8249185

# ======================
# BÀI 2: Root Mean Square Error (RMSE)
# ======================

df <- data.frame(
  t = rnorm(100),
  y = rnorm(100)
)

bai2_result <- df %>%
  { (.$t - .$y)^2 } %>%
  mean() %>%
  sqrt()

bai2_result

## [1] 1.382286