R/model1.R

In markhwhiteii/processr: R Implementation of the PROCESS Macro

#' Model 1 from the PROCESS Macro: Two-Way Interaction
#' 
#' Performs a simple two-way interaction and returns simple slopes, as per
#' Model 1 from the PROCESS Macro.
#' 
#' @param iv The name of the independent variable, as a character string.
#' @param dv The name of the dependent variable, as a character string.
#' @param mod The name of the moderator, as a character string. If the moderator
#' is numeric with only 0s and 1s, it will return the simple slopes at the values of
#' 0 and 1; if it is numeric otherwise, it will return the simple slopes at a standard
#' deviation below the mean, a standard deviation above the mean, and at the mean.
#' @param data The data frame with the relevant variables.
#' @return The coefficients, standard errors, t-statistics, and p-values of 
#' the regression coefficients table and the simple slopes.
#' @export
model1 <- function(iv, dv, mod, data) {
  coefs <- broom::tidy(stats::lm(data[, dv] ~ data[, iv] * data[, mod]))
  coefs[, 1] <- c("intercept", iv, mod, "interaction")
  
  if (all(data[, mod] == 0 | data[, mod] == 1)) {
    sss <- simple_slope(iv, dv, mod, 0, data)
    sss <- rbind(sss, simple_slope(iv, dv, mod, 1, data))
  } else {
    sss <- simple_slope(iv, dv, mod, mean(data[, mod]) - stats::sd(data[, mod]), data)
    sss <- rbind(sss, simple_slope(iv, dv, mod, mean(data[, mod]), data))
    sss <- rbind(sss, simple_slope(iv, dv, mod, mean(data[, mod]) + stats::sd(data[, mod]), data))
  }
  
  out <- rbind(coefs, sss)
  
  return(out)
}