简洁高效的R——内建函数的使用

今天看到一个很好的tutorial，学习了之后，精简地写出了以下的两个function。前一个是从基本思想出发来写，后一个是对前一个的优化版本。后者在处理数量很大的CSV文件操作时会显出优势。

weightmedian.R:

weightmedian <- function(directory, day) {
        files_full <- list.files(directory, full.names = TRUE)
        dat <- data.frame()
        
        for (i in 1:5) {
                dat <- rbind(dat, read.csv(files_full[i]))
        }
        
        dat_day <- dat[which(dat[, "Day"] == day), ]
        
        median(dat_day$Weight, na.rm = TRUE)
}

optiweightmedian <- function(directory, day) {
        files_full <- list.files(directory, full.names = TRUE)
        #tmp <- vector(mode = "list", length = length(files_full))
        tmp <- lapply(files_full, read.csv)
        dat <- do.call(rbind, tmp)
        dat_day <- dat[which(dat[, "Day"] == day), ]
        median(dat_day$Weight, na.rm = TRUE)
}

代码虽短，却足以显示出R语言的简洁高效。简单之中，往往蕴藏着大智慧。