r - 使用 read.csv 跳过 r 中的最后一列

Question

我在那个帖子上 read.csv and skip last column in R但没有找到我的答案，并尝试直接在 Answer 中检查......但这不是正确的方法(感谢 mjuarez 花时间让我回到正轨。

原来的问题是:

I have read several other posts about how to import csv files with read.csv but skipping specific columns. However, all the examples I have found had very few columns, and so it was easy to do something like:

 columnHeaders <- c("column1", "column2", "column_to_skip")
 columnClasses <- c("numeric", "numeric", "NULL")
 data <- read.csv(fileCSV, header = FALSE, sep = ",", col.names = 
 columnHeaders, colClasses = columnClasses)

所有答案都很好，但不适用于我打算做的事情。所以我问我自己和其他人:

And in one function, does data <- read_csv(fileCSV)[,(ncol(data)-1)] could work?

我试过一行 R上车 data ，前 6 列中的所有 5 列，所以不是最后一列。为此，我想在列数中使用“-”，您认为可能吗？我怎样才能做到这一点？

谢谢!

Answer 1

在基地 r它必须是2步操作。例子:

> data <- read.csv("test12.csv")
> data
# 3 columns are returned
          a b c
1 1/02/2015 1 3
2 2/03/2015 2 4

# last column is excluded 
> data[,-ncol(data)]
          a b
1 1/02/2015 1
2 2/03/2015 2

一个不会写data <- read.csv("test12.csv")[,-ncol(data)]在基地 r .

但是，如果您知道 csv 中的最大列数(在我的情况下说 3)然后可以写:

df <- read.csv("test12.csv")[,-3]
df
          a b
1 1/02/2015 1
2 2/03/2015 2