as.numeric() doesn't convert factors to the explicit value, nor should

it. Under what you're expecting, ff you have a factor where the levels

are "Female" and "Male", using as.numeric() wouldn't produce anything

meaningful.

However, as.numeric() does something much smarter. It converts "Female"

to 1, and "Male" to 2. More generally, if you have n levels, it will

produce a vector of values between 1 and n. This is referred to as the

'internal coding.'

If you want to convert your height and bmi variables to their numeric

values, you need to do

> as.numeric(as.character(height))

This will get you around the internal coding.

-----Original Message-----

From:

[hidden email] [mailto:

[hidden email]]

On Behalf Of deanj2k

Sent: Friday, May 15, 2009 7:58 AM

To:

[hidden email]
Subject: [R] help with as.numeric

hi everyone, wondering if you could help me with a novice problem. I

have a

data frame called subjects with a height and weight variable and want to

calculate a bmi variable from the two. i have tried:

attach(subjects)

bmi <- (weight)/((height/100)^2)

but it comes up with the error:

Warning messages:

1: In Ops.factor(height, 100) : / not meaningful for factors

2: In Ops.factor((weight), ((height/100)^2)) :

/ not meaningful for factors

I presume that this means the vectors height and weight are not in

numeric

form (confirmed by is.numeric) so i changed the code to:

bmi <- (as.numeric(weight))/((as.numeric(height)/100)^2)

but this just comes up with a result which doesnt make sense i.e.

numbers

such as 40000 within bmi vector. Ive looked at

as.numeric(height)/as.numeric(weight) and these numbers just arnt the

same

as height/weight which is the reason for the incorrect bmi. Cant anyone

tell me where I am going wrong? Its quiet frustrating because I cant

understand why a function claiming to convert to numeric would come up

with

such a bizarre result.

--

View this message in context:

http://www.nabble.com/help-with-as.numeric-tp23558326p23558326.htmlSent from the R help mailing list archive at Nabble.com.

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