有没有办法在 R 中将大型文档作为 data.frame 读取？

Question

I'm trying to use ggplot2 on a large data set stored into a csv file. I used to read it with excel.

I don't know how to convert this data into a data.frame . In particular, I have a date column that has the following format: "2020/04/12:12:00" . How can I get R to understand this format?

Answer 1

If it's a csv , you can use:

• fread function from data.table . This will be the fastest way to read your csv.
• read_csv or read_csv2 (for ; delimited documents) in readr package

If it's .xls (or .xlsx ) document, have a look at the readxl package.

All these functions import your data as data.frame s (with additional classes like data.table for fread or tibble for read_csv ).

Edit

Given your comment, it looks like your file is not an excel but a csv. If you want to convert a column type to date, assuming your dataframe is called df

df[, dates := as.POSIXct(get(colnames(df)[1]), format = "%Y/%m/%d:%H:%M")]

Note that you don't need to use cbind or even reassign the data.table because you use := operator

As the message is saying you, you don't need the extra-precision of POSIXlt

Answer 2

Going by the question alone, I would suggest the openxlsx package, it has helped me reduce the time significantly in reading large datasets. Three points you may find it to be helpful based on your question and the comments

• The read command stays same as xlsx package, however would suggest you to use openxlsx::read.xslx(file_path)
• the arguments are again same, but in the place of sheetIndex it is sheet and it takes only numbers
• If the existing columns are converted to character, then a simple as.Date would work