[R] numeric coercion when one or more elements is non numerice

[Gavin Simpson]

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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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