在R中写入txt时将信息行附加到data.frame的开头 [英] Appending information lines to the beginning of a data.frame when writing to txt in R

问题描述

我刚刚收到了关于在.txt输出开头添加文本行的上一个问题的一些很好的建议。这对我的示例数据效果很好，但是我现在意识到，我的实际数据有一个 POSIXlt 类的变量，它包含了日期和时间值之间的空格（例如 2001-01-01 10:00:01）。这似乎是导致R的问题，以了解他们的数据列数。对于上一个问题，我已经尝试了两种建议，但似乎没有任何效果。我甚至尝试写作.csv文件来更好地定义分隔，但这也失败了。

I just received some great advice on a previous question regarding appending text lines to the beginning of a .txt output. This worked well for my example data, but I now realize that my actual data has a variable of the POSIXltclass, which contains a space between the day and hour values (e.g. "2001-01-01 10:00:01"). This seems to be causing problems for R to understand how many columns of data their are. I have tried variations on both suggestions given to the previous question, but nothing seems to work. I even tried writing as a .csv file to better define the separations, but this also failed.

任何帮助将不胜感激。我可能在这里做一些非正统的事情吗？我应该单独制作一个readme.txt文件来包含变量描述并避免所有的这种挫败感吗？我希望数据集对于未来的用户是合乎逻辑的，不言而喻的。

Any help would be greatly appreciated. Am I perhaps doing something unorthodox here? Should I just make a separate "readme.txt" file to contain the variable descriptions and avoid all of this frustration? I want the data sets to be logical and self-explanatory to future users.

###Example dataset
Head <- 
"#variables:
#sal - Salinity [PSU]
#temp - Temperature [degrees Celsius]
#datetime - Date [yyyy-mm-dd hh:mm:ss]

"

n <- 10
df <- data.frame(sal=runif(n, 30, 37), temp=runif(n, 15, 17), datetime=as.POSIXlt("2001-01-01 10:00:01"))
df

###Create .txt (or .csv?)
#option 1
fn <- "data.txt"
sink(fn)
cat(Head)
df
sink()
read.table(fn)
#Error in scan(file, what, nmax, sep, dec, quote, skip, nlines, na.strings,  : 
#  line 1 did not have 5 elements

#option 2
fn <- "data.txt"
writeLines(Head, fn)
write.table(df, fn, append=TRUE, quote=FALSE)
#Warning message:
#In write.table(df, fn, append = TRUE, quote = FALSE) :
#  appending column names to file
read.table(fn)
#Error in scan(file, what, nmax, sep, dec, quote, skip, nlines, na.strings,  : 
#  line 1 did not have 5 elements

#option 3
fn <- "data.csv"
sink(fn)
cat(Head)
write.csv(df)
sink()
read.csv(fn, header=TRUE)
#Error in read.table(file = file, header = header, sep = sep, quote = quote,  : 
#  more columns than column names

推荐答案

您可以使用逗号（例如）而不是空格分隔数据列。你当然需要将 sep =，参数指定为 write.table（）和 read.table（）。

You can make this work by using commas (for example) instead of whitespace to separate the data columns. You'll of course then need to specify the sep="," argument to both write.table() and read.table().

（顺便提一句，额外的控件由许多可能的参数提供到 write.table（）是通常喜欢 write.table（df，...，append = TRUE）超过
sink（fn）; df; sink（）使用 sink（），data.frame以相同的方式写入文件，将其打印到控制台，减少对其表示细节的控制。）

(Incidentally, the extra control provided by the many possible arguments to write.table() is one reason to generally prefer write.table(df, ..., append=TRUE) over sink(fn); df; sink(). With sink(), the data.frame gets written to a file in same way it would be printed to the console, giving you much less control over details of its representation.)

fn <- "data.txt"
writeLines(Head, fn)
write.table(df, fn, append=TRUE, quote=TRUE, sep=",")

## Reading data from the file now works fine 
dd <- read.table(fn, header=TRUE, sep=",")
head(dd, 4)
#        sal     temp            datetime
# 1 35.28238 16.48981 2001-01-01 10:00:01
# 2 31.80891 16.68704 2001-01-01 10:00:01
# 3 32.22510 15.87365 2001-01-01 10:00:01
# 4 33.13408 16.60193 2001-01-01 10:00:01

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