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Validating data type

3 messages · jeffjohn at WorldVision.org, Jeff Newmiller, John Kane

Original
Jeff Newmiller
# 
The answer to your question is yes. You can convert a column of values to Date using the as.Date function with the appropriate format, and then test if any values are NA using the is.na function, and find them with the which function.

If you want something less vague then you should read the Posting Guide mentioned at the bottom of this message and follow the advice about using plain text and providing a sample of data that exhibits the issue and your attempts to solve the problem (code). Sample data is almost always needed... if you don't make it, then we have do so in order to illustrate the solution, but we would be guessing and that is just a waste of time. You may find the following link helpful also: http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example
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jeffjohn at WorldVision.org wrote:
John Kane
# 
It sounds like that column of data is not of type "date" at all. You cannot have one element of a column different from the rest of the column.  In a data.frame you can have different types of data in different columns but not in the same column.

Where mydata is your data.frame do :

str(mydata)

This will give you a listing of the type of data in each column in your data.frame.  

My guess would be that R has read in that column as character or factor.  Just because it looks like a date on the screen does not mean it is one. You probably will have to convert it to a date. 

See ?as.Date for one way to do this.

  You might also want to have a look at the lubridate package.

For further reference 
https://github.com/hadley/devtools/wiki/Reproducibility
 http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example

In particular for a question like yours, supplying some sample data using dput() would have really helped.  If you are still having a problem do : dput(mydata) and paste the output into the email. The reader  can then paste the data into their version of R and see exactly what you are working with.  For large datasets usually a sample amoutnt will do  , so  dput(head(mydata, 100) for example will supply 100 rows of data.

Below is a example of a data.frame in dput format. Just copy and paste it into R and you will have a new date.frame

John Kane
Kingston ON Canada

##====================dput file===================
dat1  <-  structure(list(xx = structure(c(5L, 6L, 10L, 9L, 17L, 10L, 15L, 
16L, 5L, 14L, 5L, 7L, 17L, 6L, 11L, 8L, 5L, 3L, 1L, 17L, 7L, 
10L, 5L, 15L, 15L, 16L, 17L, 14L, 8L, 13L, 12L, 13L, 18L, 9L, 
5L, 2L, 1L, 16L, 1L, 1L, 1L, 16L, 4L, 10L, 1L, 18L, 18L, 14L, 
13L, 4L), .Label = c("a", "b", "d", "f", "g", "h", "i", "j", 
"k", "l", "m", "n", "o", "p", "q", "r", "s", "t"), class = "factor"), 
    yy = c(0.332304663767243, -1.77867401940838, 0.828612337938625, 
    0.481702424196278, 0.0825987297345907, -1.40224568135063, 
    -0.243388884456876, 0.0865304079310024, -0.124012796374592, 
    -0.0107544463484595, -0.542307211820575, 0.0129727866797914, 
    -0.478553152291621, -1.63895681984396, 0.0911014618211326, 
    -0.890215628553797, -1.42140590396317, 0.202337039384179, 
    1.30089052407852, 0.07517013402338, -0.807355878474237, 1.12978841894929, 
    0.154740986108198, 0.21209595540936, 0.65345449749952, 0.533479658343466, 
    0.665882552612018, -0.604444572360781, -0.0971202279326936, 
    -0.862179166296771, -0.977706435316816, 0.559634439503645, 
    0.0320050874597674, -1.65502174652502, 0.853046541850183, 
    -0.801904205812903, -0.820335448022446, -0.912451936657161, 
    0.222469916395761, 0.0168002536713376, -0.218537143966283, 
    1.00191128410043, -0.430912734152427, -1.1327880971227, -0.664284053548425, 
    1.3082467197158, 1.46148850229679, -1.11954785811615, -1.61706514557631, 
    0.604530320200236)), .Names = c("xx", "yy"), row.names = c(NA, 
-50L), class = "data.frame")
##===================end dput file
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