[R] Strange result when subsetting a data frame based on a character variable

Karl Schilling karl.schilling at uni-bonn.de
Tue Nov 17 20:14:15 CET 2015

Dear all,

I have one observation that I do not quite understand. Maybe someone
can clarify this issue for me.

I have a data frame which I want to subset based on a grouping variable, 
say "group". Actually, "group" is a numeric value, but it is saved as a 
character. I give some code to generate an exemplary data frame below.

Now, if I use

MySubset <- subset(Data, Data$group == "..")

everything works fine, as expected. ".." stands here for the value of 
group given as a character string.

Surprisingly, I also get a correct subsetting if I simply give the plain 
numeric value of group (like MySubset <- subset(Data, Data$group == ..), 
AS LONG AS this numeric value is less then 100000.

If the numeric value is 100000 or larger, I get an empty subset.

OK, I know how to avoid this situation, but I wonder what the 
explanation for this for me rather strange behavior might be.

Thank you so much for your suggestions.

Karl Schilling

Exemplary code for reproducing the above described problem:

options(stringsAsFactors = F)

# set up some data frame
value <- c(1:6)
group <- rep(c("20000", "99999", "100000"), each = 2)
Data <- data.frame(value = value, group = group)

# subset data frame based on the value of the variable "group",
# treating this value once as a character, and once as a number:

Data20 <- subset(Data, Data$group =="20000")
Data20N <- subset(Data, Data$group ==20000)

Data99 <- subset(Data, Data$group =="99999")
Data99N <- subset(Data, Data$group ==99999)
Data100 <- subset(Data, Data$group =="100000")
Data100N <- subset(Data, Data$group ==100000)

Karl Schilling

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