从多个 CSV 文件计算一列的平均值 [英] Calculate the mean of one column from several CSV files

问题描述

我在一个文件夹(名为 001.csv、002.csv 等)中有 300 多个 CSV 文件.每个都包含一个带有标题的数据帧.我正在编写一个函数，它将接受三个参数:文件的位置、要计算平均值的列的名称(在数据框内)以及用于计算的文件.

I have over 300 CSV files in a folder (named 001.csv, 002.csv and so on). Each contains a data frame with a header. I am writing a function that will take three arguments: the location of the files, the name of the column you want to calculate the mean (inside the data frames), and the files to use in the calculation.

这是我的功能:

pollutantmean2 <- function(directory = getwd(), pollutant, id = 1:332) {

    # add one or two zeros to ID so that they match the CSV file names
    filenames <- sprintf("%03d.csv", id)

    # path to specdata folder
    # if no path is provided, default is working directory
    filedir <- file.path(directory, filenames)

    # get the data from selected ID or IDs from the specified path
    dataset <- read.csv(filedir, header = TRUE)

    # calculate mean removing all NAs
    polmean <- mean(dataset$pollutant, na.rm = TRUE)

    # return mean
    polmean

}

我的代码似乎有两处错误.为了分解它，我将函数分成两个单独的函数来处理两个任务:1) 获取所需的文件和 2) 计算所需列的平均值(又名 pollutant).

It appears there are two things wrong with my code. To break it down, I separated the function into two separate function to handle the two tasks: 1) get the required files and 2) calculate the mean of the desired column (aka pollutant).

任务 1: 获取适当的文件 - 只要我只需要一个文件，它就可以工作.如果我选择一系列文件，例如 1:25，我会收到一条错误消息，内容为 Error in file(file, "rt") : invalid 'description' argument.我在谷歌上搜索了这个错误，但仍然不知道如何修复它.

Task 1: Getting the appropriate files - It works as long as I only want one file. If I select a range of files, such as 1:25 I get an error message that says Error in file(file, "rt") : invalid 'description' argument. I have Googled this error but still have no clue how to fix it.

# function that obtains csv files and stores them
getfile <- function(directory = getwd(), id) {
    filenames <- sprintf("%03d.csv", id)
    filedir <- file.path(directory, filenames)
    dataset <- read.csv(filedir, header = TRUE)
    dataset
}

如果我运行 getfile("specdata", 1) 它工作正常，但如果我运行 getfile("specdata", 1:10) 我得到以下错误:文件中的错误(文件，rt"):无效的描述"参数.

If I run getfile("specdata", 1) it works fine, but if I run getfile("specdata", 1:10) I get the following error: Error in file(file, "rt") : invalid 'description' argument.

任务 2: 计算指定命名列的均值 - 假设我有一个可用的数据框，然后我尝试使用以下函数计算均值:

Task 2: Calculating mean of specified named column - Assuming I have a usable data frame, I then try to calculate the mean with the following function:

calcMean <- function(dataset, pollutant) {
    polmean <- mean(dataset$pollutant, na.rm = TRUE)
    polmean
}

但是如果我运行 calcMean(mydata, "sulfate")(其中 mydata 是我手动加载的数据框)，我会收到一条错误消息:警告信息:在 mean.default(dataset$pollutant, na.rm = TRUE) 中:参数不是数字或逻辑:返回 NA

But if I run calcMean(mydata, "sulfate") (where mydata is a data frame I loaded manually) I get an error message: Warning message: In mean.default(dataset$pollutant, na.rm = TRUE) : argument is not numeric or logical: returning NA

奇怪的是，如果我在控制台中运行 mean(mydata$sulfate, na.rm = TRUE)，它工作正常.

The odd thing is that if I run mean(mydata$sulfate, na.rm = TRUE) in the console, it works fine.

我已经研究了几天，经过无休止的调整，我已经没有想法了.

I have researched this for several days and after endless tweaking, I have run out of ideas.

推荐答案

您不需要更多功能.根据我的理解，解决方案可以更简单 6 行:

You do not need more functions. The solution can be simpler from my understanding in 6 lines:

pollutantmean <- function(directory, pollutant, id = 1:10) {
filenames <- sprintf("%03d.csv", id)
filenames <- paste(directory, filenames, sep="/")
ldf <- lapply(filenames, read.csv)
df=ldply(ldf)
# df is your list of data.frames
mean(df[, pollutant], na.rm = TRUE)
}

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