I am a relatively new user of R and have a question about using the
read.table command for reading in .csv files that contain dates. My
ultimate goal is to be able to read several different files into data frames
and then do a merge along the "Date" column of each data frame. It seems I
should be able to specify the name of the column that contains dates and
then automatically convert that to dates, all in a single read.table
statement. It's such a natural thing to do (and the help for read.table
gives me hope, but I have not been able to figure out some of the options,
e.g., colNames).
Here is a specific example of what I mean and what the problems are. An
First I load a sample data file whose first column is a date. This gives
the wrong answer as we shall see:
> library(date)
> sampData <- read.table("sampleData.csv",sep=",",header=TRUE)
> sampData
Date Col1 Col2 Col3
1 1/1/2003 1.2 1.4 0.160
2 1/4/2003 1.8 1.2 0.900
3 1/5/2003 0.9 1.1 -0.003
> mode(sampData$Date)
[1] "numeric"
>
Note that the Date column is coerced incorrectly into being numeric. Right
now what I do is force R to read this in as a character using "as.is" and
then convert it to a date as follows:
> sampData <- read.table("sampleData.csv",sep=",",header=TRUE,as.is=1)
> sampData
Date Col1 Col2 Col3
1 1/1/2003 1.2 1.4 0.160
2 1/4/2003 1.8 1.2 0.900
3 1/5/2003 0.9 1.1 -0.003
> mode(sampData$Date)
[1] "character"
> sampData$Date <- as.date(sampData$Date)
> sampData
Date Col1 Col2 Col3
1 15706 1.2 1.4 0.160
2 15709 1.8 1.2 0.900
3 15710 0.9 1.1 -0.003
>
Now the Data column is converted to Julian, which is good b/c if I repeat
this procedure with other dataframes I can do a merge on the date columns
and line up the dates. But, there are two drawbacks with this approach
which I do not know how to solve:
1. it's generally clumsy and takes too many lines.
2. (more importantly) it forces me to specify which column number contains
the dates instead of simply stating which column header name contains date.
I would rather simply the column header name of the column that contains the
date (in this example: Date) so that whichever column contains the date will
be automatically converted to dates.
So, is there a way to specify that I want the column labeled "Date" to be
read as a date class (as in as.date)?
Any hints will be much appreciated.
Neil Chriss
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