R help - Nov 2016 - about data structure

Hi R users,

I'm wondering why the values changed when I try to transform factors into
numerics.

For example, for a data frame DF, there is one column called precipitation,
which is usually lower than 100mm. But this column is factor when I read in
the data. When transform to numeric values, some rows can be higher than
1000mm. What is the problem? Thanks.

DF$prec_new = as.numeric(DF$precip)

	[[alternative HTML version deleted]]

Hello,

Try

as.numeric(as.character(DF$precip))

Hope this helps,

Rui Barradas

Em 07-11-2016 20:24, lily li escreveu:
> Hi R users,
>
> I'm wondering why the values changed when I try to transform factors
into
> numerics.
>
> For example, for a data frame DF, there is one column called precipitation,
> which is usually lower than 100mm. But this column is factor when I read in
> the data. When transform to numeric values, some rows can be higher than
> 1000mm. What is the problem? Thanks.
>
> DF$prec_new = as.numeric(DF$precip)
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

You have non-numeric data somewhere in that column, and factor is already a
numeric type (Read about factors in the Introduction to R document that comes
with R). Try

DF$prec_new = as.numeric(as.character (DF$precip)

and then look at

DF$precip[ is.na( DF$precip_new ) ]

to see which values are corrupt. Eliminating the whole factor conversion in the
first place might be as simple as adding an na.string argument to your
read.table or read.csv call that imports the data.

If you need further help, next time send plain text format email with a
reproducible example.

http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example

http://adv-r.had.co.nz/Reproducibility.html
-- 
Sent from my phone. Please excuse my brevity.

On November 7, 2016 12:24:57 PM PST, lily li <chocold12 at gmail.com>
wrote:
>Hi R users,
>
>I'm wondering why the values changed when I try to transform factors
>into
>numerics.
>
>For example, for a data frame DF, there is one column called
>precipitation,
>which is usually lower than 100mm. But this column is factor when I
>read in
>the data. When transform to numeric values, some rows can be higher
>than
>1000mm. What is the problem? Thanks.
>
>DF$prec_new = as.numeric(DF$precip)
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.