There is a phenomenon that occurs here which, it seems to me,
merits some emphasis. The glm() function appears to be perfectly
willing to take a variable of class "Date" and treat it as a continuous
variable.
Apparently what it does (on the basis of one little experiment that I
did) is convert the vector of dates to a vector of "Julian date" values,
taking the origin to be the minimum value of the Date vector.
I would have thought that the user would have to effect this conversion
her/himself. But not so; the software is so cleverly written that it's all
handled for the user.
The designers of R have thought of just about *everything*!
We think it 'mazing! :-)
cheers,
Rolf Turner
On 04/11/12 14:58, jim holtman wrote:
Here is how to convert your column of factors into Dates:
x <- read.table(text = '2/10/2011
+ 2/20/2011
+ 3/4/2011')
# read in as factors
str(x)
'data.frame': 3 obs. of 1 variable:
$ V1: Factor w/ 3 levels "2/10/2011","2/20/2011",..: 1 2 3
# convert to Date
x$date <- as.Date(as.character(x$V1), format = "%m/%d/%Y")
x
V1 date
1 2/10/2011 2011-02-10
2 2/20/2011 2011-02-20
3 3/4/2011 2011-03-04
str(x)
'data.frame': 3 obs. of 2 variables:
$ V1 : Factor w/ 3 levels "2/10/2011","2/20/2011",..: 1 2 3
$ date: Date, format: "2011-02-10" "2011-02-20" "2011-03-04"
On Sat, Nov 3, 2012 at 8:09 PM, hoguejm <hogu...@gmail.com> wrote:
I am very new to R, so I apologize if this question is trivial.
I have a row in my data of dates in the format mm/dd/yyyy; about 3500 rows.
I am using this variable in a logistic regression model, and need to treat
it as continuous, not a factor as r has decided it is.
I tried the as.numeric function but it resulted in all NA's and the message:
"NAs introduced by coercion"
If anyone knows a solution, I would greatly appreciate it.
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