R help - Jun 2014 - A Question about read.table and Data Frames in R

I created the following file:

symbol,shares
XOM,1000
APA,400
CVX,200

I then read the file in R using the command:
	stockList=read.table("/NotesOnR/stockList", header = T,
sep=",")

I would then expect the following expression to evaluate to the simple
string APA:
	stockList$symbol[2]
However when I type that in on the command line, I get:
[1] APA
Levels: APA CVX XOM

I would also expect to be able to print out the table by using the command:
	for( i in 1:3 ) {
		print( stockList$symbol[i] )
		print ( stockList$shares[i] )
	}

However, as part of the output I get:
	Levels: APA CVX XOM
I do not understand what is going on. Also, when I try passing the
expression stockList$symbol to a standard function in R, it does not work.

I think that I am missing something here but I am not sure what I am
missing. Should I be writing code like:
	for  ( i in stockList$smybol )
However,  given the symbol, I am not sure how to get the share count that is
in the same row.

I thank the group in advance for their responses.

Bob

On Jun 29, 2014, at 3:22 PM, Robert Sherry wrote:
> I created the following file:
>
> symbol,shares
> XOM,1000
> APA,400
> CVX,200
>
> I then read the file in R using the command:
> 	stockList=read.table("/NotesOnR/stockList", header = T,
sep=",")
>
> I would then expect the following expression to evaluate to the simple
> string APA:
> 	stockList$symbol[2]
> However when I type that in on the command line, I get:
> [1] APA
> Levels: APA CVX XOM
>
> I would also expect to be able to print out the table by using the  
> command:
> 	for( i in 1:3 ) {
> 		print( stockList$symbol[i] )
> 		print ( stockList$shares[i] )
> 	}
>
> However, as part of the output I get:
> 	Levels: APA CVX XOM
> I do not understand what is going on. Also, when I try passing the
> expression stockList$symbol to a standard function in R, it does not  
> work.
>
> I think that I am missing something here but I am not sure what I am
> missing.
You are missing the fact that a factor variable was created. If you  
had added stringsAsFactors=FALSE to your read.table code, you would  
ahve gotten what you expected.

> Should I be writing code like:
> 	for  ( i in stockList$smybol )
> However,  given the symbol, I am not sure how to get the share count  
> that is
> in the same row.
>
> I thank the group in advance for their responses.
>
> Bob
>
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David Winsemius, MD
Alameda, CA, USA