[R] numeric coercion when one or more elements is non numerice
Gavin Simpson
gavin.simpson at ucl.ac.uk
Wed Jan 30 17:22:57 CET 2008
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On Wed, 2008-01-30 at 07:53 -0800, Arthur Steinmetz wrote:
> I don't understand this behavior. Why does the every data point get
> trashed by data.matrix when there is one non-numeric element in the
> array? Thanks.
I suspect it is because your data GDP variable is not what you think it
is. What does str(temp) say about GDP? I'll guess it says something like
this:
> str(temp)
'data.frame': 4 obs. of 2 variables:
$ GDP : Factor w/ 4 levels "2042.4","2052.5",..: 4 3 2 1
$ CPIYOY: Factor w/ 4 levels "0.8","0.9","1.1",..: 4 2 1 3
which indicates that GDP is a factor.
As this shows, if GDP is numeric then data.matrix does produce what you
want. If GDP is a factor however, you get the behaviour you observe.
> temp <- data.frame(GDP = c(2098.1, 2085.4, 2052.5, 2042.4), CPIYOY =
c("garbage", "0.9", "0.8", "1.1"))
> str(temp)
'data.frame': 4 obs. of 2 variables:
$ GDP : num 2098 2085 2052 2042
$ CPIYOY: Factor w/ 4 levels "0.8","0.9","1.1",..: 4 2 1 3
> temp
GDP CPIYOY
1 2098.1 garbage
2 2085.4 0.9
3 2052.5 0.8
4 2042.4 1.1
> data.matrix(temp)
GDP CPIYOY
[1,] 2098.1 4
[2,] 2085.4 2
[3,] 2052.5 1
[4,] 2042.4 3
> temp2 <- temp
> temp2$GDP <- as.factor(temp2$GDP)
> data.matrix(temp)
GDP CPIYOY
[1,] 4 4
[2,] 3 2
[3,] 2 1
[4,] 1 3
One option could be to convert anything in $CPIYOY that is "garbage" to
NA, and having made sure that temp$GDP is numeric and not a factor, then
use data.matrix, which will now do what you want.
> temp$CPIYOY[temp$CPIYOY == "garbage"] <- NA
> temp
GDP CPIYOY
1 2098.1 <NA>
2 2085.4 0.9
3 2052.5 0.8
4 2042.4 1.1
> data.matrix(temp)
GDP CPIYOY
[1,] 2098.1 NA
[2,] 2085.4 2
[3,] 2052.5 1
[4,] 2042.4 3
If temp$GDP is a factor, you can't just do as.numeric(temp$GDP) as this
will result in the same behaviour as data.matrix. You need to convert to
character then to numeric:
> temp2$GDP <- as.numeric(as.character(temp2$GDP))
> temp2
GDP CPIYOY
1 2098.1 <NA>
2 2085.4 0.9
3 2052.5 0.8
4 2042.4 1.1
> data.matrix(temp2)
GDP CPIYOY
[1,] 2098.1 NA
[2,] 2085.4 2
[3,] 2052.5 1
[4,] 2042.4 3
HTH
G
>
>
> > temp
>
> GDP CPIYOY
>
> 19540 2098.1 garbage
>
> 19632 2085.4 0.9
>
> 19724 2052.5 0.8
>
> 19814 2042.4 1.1
>
>
> > data.matrix(temp)
>
> GDP CPIYOY
>
> 19540 4 4
>
> 19632 3 2
>
> 19724 2 1
>
> 19814 1 3
>
> >
>
>
>
> I'd like garbage to become NA but I tried filtering the array to scrub
> the data but it has no effect. This illustrates it:
>
> > temp[1,2] <- NA
>
> > temp
> GDP CPIYOY
> 19540 2098.1 <NA>
> 19632 2085.4 0.9
> 19724 2052.5 0.8
> 19814 2042.4 1.1
>
> > data.matrix(temp)
> GDP CPIYOY
> 19540 4 NA
> 19632 3 2
> 19724 2 1
> 19814 1 3
> >
> -- Art Steinmetz
>
>
>
>
>
>
>
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Dr. Gavin Simpson [t] +44 (0)20 7679 0522
ECRC, UCL Geography, [f] +44 (0)20 7679 0565
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