Take a data frame and some columns, return copy of data frame with centered version of those columns (with 'C' appended to colnames)

center_predictors.R

center_predictors = function(data, predictors) {
  if (!require('dplyr')) stop("Dplyr required")
  require('lazyeval')
  
  dots = list()
  for (i in seq_along(predictors)) {
    name = paste0(predictors[i], "_C")
    if (is.factor(data[[predictors[i]]])) {
      if (length(levels(data[[predictors[i]]])) > 2) stop("'", predictors[i], "' is a factor with more than 2 levels, cannot center.")
      message("'", predictors[i], "' is a factor, will convert so that '", levels(data[[predictors[i]]])[2], "' will be 'positive'.")
    } else if (is.character(data[[predictors[i]]])) {
      stop("'", predictors[i], " is character, unsure how to center. Please convert to nummeric or factor.")
    }
    dots[[name]] = interp(~as.numeric(PRED) - mean(as.numeric(PRED), na.rm = TRUE), PRED = as.name(predictors[i]))
  }
  
  data %>% 
    ungroup() %>%
    mutate_(.dots = dots)
  
}