[R] Selecting initial numerals

[joris meys]

On Tue, Oct 13, 2009 at 6:48 PM, PDXRugger <J_R_36 at hotmail.com> wrote:
>
> II just want to create a new object with the first two numerals of the data.
> Not sure why this isnt working, consider the following:
>
> EmpEst$naics=c(238321, 624410, 484121 ,238911, 811111, 531110, 621399,
> 541613,
> 524210 ,236115 ,811121 ,236115 ,236115 ,621610 ,814110 ,812320)
>
>
> EmpEst$naics2<-formatC(EmpEst$naics %% 1e2, width=2, flag="", mode
> ="integer")
> #RESULT:Warning message:
> #In Ops.factor(EmpEst$naics, 100) : %% not meaningful for factors

Wild guess : you get this warning EmpEst$naics is a factor? Quite some
errors and warnings mean mostly what they say. If you see similar
errors or warnings, please use the function str() first to check your
data structure. For example :

str(EmpEst$naics)

You should also make sure you provide us with self contained,
reproducible code. As we don't have the dataframe EmpEst, I cannot run
the code you sent. If I change it, I don't get the error.

Below a few code snippets to illustrate how the problem arises, and
how to get it away :

> naics=c(238321, 624410, 484121 ,238911, 811111, 531110, 621399,541613,
+ 524210 ,236115 ,811121 ,236115 ,236115 ,621610 ,814110 ,812320)
>
> naics2<-formatC(naics %% 1e2, width=2, flag="", mode
+ ="integer")
> naics2
 [1] "21" "10" "21" "11" "11" "10" "99" "13" "10" "15" "21" "15" "15" "10" "10"
[16] "20"

No error, as vector naics is a numerical vector. I make it a factor :

> naics=factor(c(238321, 624410, 484121 ,238911, 811111, 531110, 621399,541613,
+ 524210 ,236115 ,811121 ,236115 ,236115 ,621610 ,814110 ,812320))
>
> naics2<-formatC(naics %% 1e2, width=2, flag="", mode
+ ="integer")
Warning message:
In Ops.factor(naics, 100) : %% not meaningful for factors
> naics2
 [1] "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA" "NA"
[16] "NA"

Which is what you see. You can transform a factor to a numerical
vector with a combination of as.numeric(as.character()). This is
necessary as you would otherwise get the internal values for the
factor levels (i.e. the numbers 1, 2, ... n with n being the number of
levels.)

> naics=factor(c(238321, 624410, 484121 ,238911, 811111, 531110, 621399,541613,
+ 524210 ,236115 ,811121 ,236115 ,236115 ,621610 ,814110 ,812320))
>
> naics2<-formatC(as.numeric(as.character(naics)) %% 1e2, width=2, flag="", mode
+ ="integer")
> naics2
 [1] "21" "10" "21" "11" "11" "10" "99" "13" "10" "15" "21" "15" "15" "10" "10"
[16] "20"