计算一系列csv文件的行数 [英] Counting the number of rows of a series of csv files

问题描述

我正在研究R教程，并且怀疑我必须使用这些功能之一，但是我不确定是哪一个(是的，我已经研究了它们，但是直到我对R术语更加流利时，它们才变得令人困惑). /p>

在我的工作目录中有一个文件夹"specdata". Specdata包含数百个名为001.csv-300.csv的CSV文件.

我正在使用的函数必须计算输入的csv文件的总行数.因此，如果函数中的参数为1:10并且每个文件都有十行，则返回100.

这是我到目前为止所拥有的:

complete <- function(directory,id = 1:332) {
    setpath <- paste("/Users/gcameron/Desktop",directory,sep="/")
    setwd(setpath)
    csvfile <- sprintf("%03d.csv", id)
    file <- read.csv(csvfile)
    nrow(file)
 }

当ID参数为一个数字(例如17)时，此方法有效.但是，如果我输入10:50作为参数，则会收到错误消息:

Error in file(file, "rt") : invalid 'description' argument

我该怎么做才能从输入的ID参数计算总行数?

解决方案

read.csv期望只读取一个文件，因此您需要循环遍历文件，一种惯用的方法是使用sapply:

nrows <- sapply( csvfile, function(f) nrow(read.csv(f)) )
sum(nrows)

例如，这是您的complete函数的重写:

complete <- function(directory,id = 1:332) {
    csvfiles <- sprintf("/Users/gcameron/Desktop/%s/%03d.csv", directory, id)
    nrows <- sapply( csvfiles, function(f) nrow(read.csv(f)) )
    sum(nrows)
}

I'm working through an R tutorial and suspect that I have to use one of these functions but I'm not sure which (Yes I researched them but until I become more fluent in R terminology they are quite confusing).

In my working directory there is a folder "specdata". Specdata contains hundreds of CSV files named 001.csv - 300.csv.

The function I am working on must count the total number of rows for an inputed number of csv files. So if the argument in the function is 1:10 and each of those files has ten rows, return 100.

Here's what I have so far:

complete <- function(directory,id = 1:332) {
    setpath <- paste("/Users/gcameron/Desktop",directory,sep="/")
    setwd(setpath)
    csvfile <- sprintf("%03d.csv", id)
    file <- read.csv(csvfile)
    nrow(file)
 }

This works when the ID argument is one number, say 17. But, if I input say 10:50 as an argument, I receive an error:

Error in file(file, "rt") : invalid 'description' argument

What should I do to be able to count the total number of rows from the inputed ID parameter?

解决方案

read.csv expects to read just one file, so you need to loop over files, a R idiomatic way of doing so is to use sapply:

nrows <- sapply( csvfile, function(f) nrow(read.csv(f)) )
sum(nrows)

For example, here is a rewrite of your complete function:

complete <- function(directory,id = 1:332) {
    csvfiles <- sprintf("/Users/gcameron/Desktop/%s/%03d.csv", directory, id)
    nrows <- sapply( csvfiles, function(f) nrow(read.csv(f)) )
    sum(nrows)
}

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