[R] Select first element of each factor and convert to NA

[PIKAL Petr]

Hi

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Cesar Terrer
> Sent: Friday, March 01, 2013 4:21 AM
> To: r-help at r-project.org
> Subject: [R] Select first element of each factor and convert to NA
> 
> Hi all,
> 
> 
> 
> I have a dataframe of the following type:
> 
> 
> 
> Day        Place     dendrometer    max
> 
> 1              1                              1              4684
> 
> 2              1                              1              4831
> 
> ..
> 
> 1              1                              2              2486
> 
> 2              1                              2              2596
> 
> .
> 
> 1              2                              1              6987
> 
> 2              2                              1              6824
> 
> 
> 
> I need  the first element of each dendrometer  as NA, so every time R
> calculates "max" for a new dendrometer (independently of the place),
> starts with NA,  like this:
> 
> 
> 
> Day        Place     dendrometer    max
> 
> 1              1                              1              NA
> 
> 2              1                              1              4831
> 
> ..
> 
> 1              1                              2              NA
> 
> 2              1                              2              2596
> 
> .
> 
> 1              2                              1              NA
> 
> 2              2                              1              6824
> 

Just as a curiosity, do you want to change max value for a Day 1 to NA? If yes, 

DF$max[DF$Day==1] <- NA

shall work.

> 
> 
> Could you also let me know I could calculate MEAN of the max column for
> each dendrometer within each ring (sapply, aggregate?) instead of
> calculating mean for the entire max column?

?aggregate or maybe ?ave

Regards
Petr

> 
> 
> 
> Thanks!
> 
> 
> 
> 
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> 
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