[R] Numeric data not numeric in .csv file

[R. Michael Weylandt]

On Wed, May 2, 2012 at 4:34 AM, Jim Lemon <jim at bitwrit.com.au> wrote:
> On 05/02/2012 10:47 AM, Eve Proper wrote:
>>
>> I am a raw novice to R, playing around with a mini .csv dataset created in
>> Excel. I can read it in and the data looks OK in Excel and upon initial
>> inspection in R:
>>
>> hikes<- read.csv("/Users/eproper/Desktop/hikes.csv", header=TRUE)
>> print(hikes)
>>
>> does exactly what it is supposed to do.
>>
>> Two of the variables are genuine strings, but the others ought to be
>> numeric, and R will calculate their min, max etc. However, is.numeric
>> returns FALSE for all of them; storage.mode returns "language." as.numeric
>> returns "Error: 'pairlist' object cannot be coerced to type 'double'." In
>> what I suspect is a related problem, any command that calls for a variable
>> name requires an initial ~ to work. That is, instead of plot(miles) I have
>> to use plot(~miles).
>>
>> No doubt there is some very elementary mistake I am making, but I can't
>> figure it out. Any help would be appreciated.
>>
> Hi Eve,
> Have you tried "as.numeric" on them? As Jeff suggested, you may be importing
> spaces along with the digits or some other character that changes the class
> of the variable. Also note that the default behavior of functions like
> read.csv is to coerce all of the values in a column of the resulting data
> frame to the "lowest common denominator". If you have one text value in a
> column of numbers, you usually get factor values. This is due to the
> restriction that all values in a column must be of the same class (data
> type).
>
> Jim
>

If accidentally coerced to factors, the OP might prefer

as.numeric(as.character(x))

to get the apparent numeric values rather than the internal ones.

Also seconded Jeff's advice about str()

Michael