or not using transform at all:
data1 <- airquality
data1$Date <- as.Date("1950-01-01")
# or in just one line:
data1 <- replace(airquality, "Date", as.Date("1950-01-01"))
On Tue, Dec 23, 2008 at 9:06 AM, Gavin Simpson <gavin.simp...@ucl.ac.uk> wrote:
> On Tue, 2008-12-23 at 05:24 -0800, Tom La Bone wrote:
>> I would like to add a column to the airquality dataset that contains the date
>> 1950-01-01 in each row. This method does not appear to work:
>>
>> > attach(airquality)
>> > data1 <- transform(airquality,Date=as.Date("1950-01-01"))
>>
>> Error in data.frame(list(Ozone = c(41L, 36L, 12L, 18L, NA, 28L, 23L, 19L, :
>> arguments imply differing number of rows: 153, 1
>>
>> I can't decipher what the error message is trying to tell me. Any
>> suggestions on how to do this?
>
> It says that the two arguments have different numbers of observations.
> The reason for which should now be pretty obvious as you provided a
> single Date whereas airquality has 153 observations.
>
> You did read ?transform , which points out this "problem"? ;-)
>
> Anyway, don't assume R recycles everything if it is not of sufficient
> length to match other arguments. In this case, repeat the date as many
> times as there are rows in airquality:
>
>> data(airquality)
>> data1 <- transform(airquality, Date = rep(as.Date("1950-01-01"),
> nrow(airquality)))
>> head(data1)
> Ozone Solar.R Wind Temp Month Day Date
> 1 41 190 7.4 67 5 1 1950-01-01
> 2 36 118 8.0 72 5 2 1950-01-01
> 3 12 149 12.6 74 5 3 1950-01-01
> 4 18 313 11.5 62 5 4 1950-01-01
> 5 NA NA 14.3 56 5 5 1950-01-01
> 6 28 NA 14.9 66 5 6 1950-01-01
>
> Also, the attach(airquality) call in your example doesn't do anything
> that affects your example so is redundant.
>
> HTH
>
> G
>
> --
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> Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> ECRC, UCL Geography, [f] +44 (0)20 7679 0565
> Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
> Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
> UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
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>
>
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