## ----setup, include=FALSE-----------------------------------------------------
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  warning = FALSE,
  message = FALSE,
  eval = requireNamespace("pwr", quietly = TRUE)
)

options(digits = 4L, knitr.kable.NA = "")

set.seed(123)

## -----------------------------------------------------------------------------
# library(pwr)
# library(effectsize)

## -----------------------------------------------------------------------------
# t <- t.test(mpg ~ am, data = mtcars)

## ----eval = FALSE-------------------------------------------------------------
# pwr.t2n.test(
#   n1 = ..., n2 = ...,
#   d = ...,
#   sig.level = ...,
#   power = ...,
#   alternative = ...
# )

## ----eval = FALSE-------------------------------------------------------------
# t_alt <- t.test(mtcars$mpg[mtcars$am == 0], mtcars$mpg[mtcars$am == 1])
# 
# effectsize(t_alt, type = "cohens_d")

## ----eval = FALSE-------------------------------------------------------------
# cohens_d(mpg ~ am, data = mtcars)

## -----------------------------------------------------------------------------
# t_to_d(
#   t = t$statistic,
#   df_error = t$parameter
# )

## -----------------------------------------------------------------------------
# (result <- cohens_d(mpg ~ am, data = mtcars))
# (Ns <- table(mtcars$am))
# 
# pwr.t2n.test(
#   n1 = Ns[1], n2 = Ns[2],
#   d = result[["Cohens_d"]],
#   sig.level = 0.05,
#   alternative = "two.sided"
# )