[R] Basic Q on coercing factors in data frames to numeric
Roger D. Peng
rpeng at jhsph.edu
Wed Nov 10 14:20:27 CET 2004
I believe this is a FAQ. See
http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-do-I-convert-factors-to-numeric_003f
-roger
Robert Brown FM CEFAS wrote:
> Hi there,
>
> I'm running R 2.0.0 on Windows 95. I'm trying to coerce a column of factors within a data frame to numeric. This is not a problem with a vector, but I can't find a way to index a column within a data frame to achieve this. All the examples from 'An introduction to R', 'S-plus 6 programmers guide', etc, use simple vectors. I'm sure I'm missing something obvious but I can't find a way to change a single column in data frame. Ive tried several approaches: here is one
>
>
>>summary(test)
>
> age yrclass weight year
> 1 :10 1992 :10 Min. :0.005333 Min. :1993
> 2 :10 1989 : 9 1st Qu.:0.221790 1st Qu.:1995
> 3 :10 1990 : 9 Median :0.413411 Median :1997
> 4 :10 1991 : 9 Mean :0.420119 Mean :1997
> 5 :10 1988 : 8 3rd Qu.:0.559819 3rd Qu.:2000
> 6 :10 1993 : 8 Max. :1.189000 Max. :2002
> (Other):82 (Other):89
>
>>contents(test)
>
>
> Data frame:test 142 observations and 4 variables Maximum # NAs:0
>
> Levels Storage
> age 23 integer
> yrclass 28 integer
> weight double
> year double
>
> +--------+---------------------------------------------------------------------+
> |Variable|Levels |
> +--------+---------------------------------------------------------------------+
> | age |0,1,10,11,12,13,14,15,16,18,19,2,20,21,24,25,3,4,5,6,7,8,9 |
> +--------+---------------------------------------------------------------------+
> | yrclass|1969,1974,1975,1978,1979,1980,1981,1982,1983,1984,1985,1986,1987,1988|
> | |1989,1990,1991,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002|
> +--------+---------------------------------------------------------------------+
>
>>is(test$yrclass,"factor")
>
> [1] TRUE
>
>>is(test$yrclass,"numeric")
>
> [1] FALSE
>
>>as(test[,2],"numeric")
>
> [1] 1 1 2 3 3 4 5 6 6 6 7 7 8 8 8 8 9 9 9 9 10 10 10 10 10
> [26] 10 10 11 11 11 11 11 12 12 12 12 12 12 12 13 13 13 13 13 13 13 14 14 14 14
> [51] 14 14 14 14 15 15 15 15 15 15 15 15 15 16 16 16 16 16 16 16 16 16 17 17 17
> [76] 17 17 17 17 17 17 18 18 18 18 18 18 18 18 18 18 19 19 19 19 19 19 19 19 20
> [101] 20 20 20 20 20 20 20 21 21 21 21 21 21 21 21 22 22 22 22 22 22 22 23 23 23
> [126] 23 23 23 24 24 24 24 24 25 25 25 25 26 26 27 27 28
>
>>is(test$yrclass,"numeric")
>
> [1] FALSE
>
>
> Regards,
>
> Robert Brown
>
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--
Roger D. Peng
http://www.biostat.jhsph.edu/~rpeng/
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