Why Numeric Values Become Factors in Data Frame
On Nov 29, 2011, at 2:18 PM, Rich Shepard wrote:
I have a data frame with 1 factor, one date, and 37 numeric values:
str(waterchem)
'data.frame': 3525 obs. of 39 variables:
site : Factor w/ 64 levels "D-1","D-2","D-3",..: 1 1 1 1 1 ...
$ sampdate : Date, format: "2007-12-12" "2008-03-15" ...
$ CO3 : num 1 1 6.7 1 1 1 1 1 1 1 ...
$ HCO3 : num 231 228 118 246 157 208 338 285 260 240 ...
$ Ca : num 100 88.4 63.4 123 78.2 103 265 213 178 166 ...
$ DO : num 4.96 9.91 4.32 2.58 1.81 5.09 3.98 5.46 1.9
2.52 ...
...
$ SC : Factor w/ 841 levels "1.090","10.000",..: 635 638 363
All the numeric categories are read in as numbers except for some
of those
in column 'SC'. I have been looking in the source file for a couple
of hours
trying to learn why values such as 1.090 and 10.000 are seen as
characters
rather than numbers. I've not see the reason.
The source file is 860K and looks like this:
site|sampdate|'Ag'|'Al'|'CO3'|'HCO3'|'Alk-
Tot
'|
'As
'|
'Ba
'|
'Be
'|
'Bi
'|
'Ca
'|
'Cd
'|
'Cl
'|'Co'|'Cr'|'Cu'|'DO'|'Fe'|'Hg'|'K'|'Mg'|'Mn'|'Mo'|'Na'|'NH4'|'NO3-
NO2'|'Oil-
grease'|'Pb'|'pH'|'Sb'|'SC'|'Se'|'SO4'|'Sr'|'TDS'|'Tl'|'V'|'Zn'
'D-1'|'2007-12-12'|0.000|0.106|1.000|231.000|231.000|0.011|0.000|
0.002|0.000|100.000|0.000|1.430|0.000|0.006|0.024|4.960|4.110|NA|
0.000|9.560|0.035|0.000|0.970|0.010|0.293|NA|0.025|7.800|0.001|
630.000|0.001|65.800|0.000|320.000|0.001|0.000|11.400
'D-1'|'2008-03-15'|0.000|0.080|1.000|228.000|228.000|0.001|0.000|
0.002|0.000|88.400|0.000|1.340|0.000|0.006|0.014|9.910|0.309|0.000|
0.000|9.150|0.047|0.000|0.820|0.224|0.020|NA|0.025|7.940|0.001|
633.000|0.001|75.400|0.000|300.000|0.001|0.000|12.400
The R command used to create the data frame is:
waterchem <- read.table('wqR.txt', header = TRUE, sep = '|')
Pointers on how to determine why this one variable has some values
and
characters rather than as numerics are needed.
So what does this show?
grep("[^0-9.]", waterchem$SC)
David Winsemius, MD
West Hartford, CT