How can I correctly access a string element of a dataframe?

1. m2q already is a data frame, so the m2qldf statement that follows
is completely unnecessary.

2. Please read ?read.table carefully, and especially the bit about the
stringsAsFactors argument. The problem is that by default character
strings are read in as factors, not characters strings. So you can
either change the way they are read in thru stringsAsFactors=FALSE or
otherwise as explained therein -- or convert them with as.character()
when you access them, e.g.

On Thu, Jul 26, 2012 at 7:53 AM, jpm miao <miaojpm at gmail.com> wrote:

Dear All,



  I would like to read the data file via read.csv (the 3rd line of the
following program) and the file name is stored in a dataframe. Since I have
several files to read, I store the file names as well as the sample period
inside a file ?B_M2Q.csv? and I read the file name first, and then read the
data file.



  The content of the file "B_M2Q.csv" is

  FX

"A_FX_M.csv"

"1981-01"

"2012-06"

Int

"A_Int.csv"

"1970-01"

"2012-03"

  (The file is attached to this email)


  The three-line program is as follows:


m2q<-read.csv(file="B_M2Q.csv", header=FALSE)  # Read the file containing
file names and sampling periods of numerical data

m2qdf<-as.data.frame(m2q)   #Make the file of filenames a dataframe
  # Read the numerical data

Nevertheless, there is an error when I  attempt to read the numerical data

x1<-read.csv(file=m2qdf[1,2])

Error in read.table(file = file, header = header, sep = sep, quote = quote,
:

  'file' must be a character string or connection

It is a problem of the file name , since I can read the data smoothly if I
change the line to

x1<-read.csv(file="A_FX_M.csv")

Could someone tell me what the problem is?
How can modify the orignal program so that I can store the sampling periods
and filenames in a dataframe, and then I read it?
How can I correctly access a string element of a dataframe?

Thanks,

Miao

--

Bert Gunter
Genentech Nonclinical Biostatistics

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