[R] Odp: Extract rows with non-zero elements

Petr PIKAL petr.pikal at precheza.cz
Tue May 4 11:21:32 CEST 2010


r-help-bounces at r-project.org napsal dne 04.05.2010 09:50:28:

> Dear all,
> In my dataset I have 12 columns and 5824 rows. The second column 
> information about the height of a claim: it might be zero or positive. I
> would like to do an analysis on the positive part of this matrix, but I 
> need the other colums with this. So if there are like 1000 rows where 
> second column is positive, I would like to extract this 1000x13 matrix 
> another matrix.
> The beginning of my code is:
> Cars <- read.csv(filename, header=TRUE, row.names=NULL, sep=";")
> attach(Cars)

Do not do that. you will have troubles with referencing objects and 
changing them, unless you perfectly know which object you 

> n <- as.numeric(n)
> s <- as.numeric(s)

you either have n and s as numeric than there is no need for as.numeric or 
they come aout as factors and in that case you get numerical 
***representation*** of levels, which is probably not what you want.

> # et cetera, the other variabeles are declared as numeric or as factors
> # I've tried to extract the data the following way:
> Cars2 <- Cars[Cars$s!=0]

see ?"[" and matrix/data.frame indexing

Cars2 <- Cars[Cars$s!=0, ]

> #However, then I get the error message:
> Error in `[.data.frame`(Cars, Cars$s != 0) : undefined columns selected
> # If I try 
> s[s!=0]
> # I do get the positive s-values, but how can I get all colums in a 

Cars is ***not*** matrix but data.frame. Seems to be minor difference but 
it is like mountain bike and racing bike. They look similar but their use 
and properties are quite different.


> Does anyone know how this can be done? Your help would be greatly
> appreciated.
> Regards,
> Frank van Berkum
> -- 
> View this message in context: 
> non-zero-elements-tp2125128p2125128.html
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