[R] R help..subsetting data frame that meeting multiple criteria

[David Winsemius]

On Nov 23, 2012, at 1:14 PM, prasmas wrote:

> Hi,
> I am new to R.  I am trying to regroup data frame using multiple  
> constrains.
> for example
>
> data frame: data
>  value	class	percent
> 15526	36	4.6875
> 15527	62	85.9375
> 15527	82	32.4564
> 15528	36	70.3125
> 15528	62	9.375
> 15528	82	74.6875
>
> I need to regroup each class that have greater than or equal to 70  
> percent
> into new group. Similarly, I also need to regroup each class that  
> have less
> than 70 percent into new group.
>
> I can do this by using following syntax for each class
> class36<- data[data$class==36&data$percent>70,]
> class36a<- data[data$class==36&data$percent<=70,]
> but I have 100 different classes. In order to do this for all 100  
> classes, I
> have write that syntax 100 times. There would be some way to do  
> dynamically
> to regroup for 100 classes (may be using for loop) but I dont know.  
> Can you
> please help in this.
> Output should be like
> data frame: class36
> value	class	percent
> 15528	36	70.3125
>
> data frame: class36a
> value	class	percent
> 15526	36	4.6875
>
 > dat.a <- dat[ dat[["class"]] %in% dat[ dat[["percent"]] >70,  
"class"] , ]
 > dat.a
   value class percent
1 15526    36  4.6875
2 15527    62 85.9375
3 15527    82 32.4564
4 15528    36 70.3125
5 15528    62  9.3750
6 15528    82 74.6875

 > row.names(dat.a) <- unlist(tapply(dat.a$class, dat.a$class,  
function(x) paste0(x, letters[1:length(x)])))
 > dat.a
     value class percent
36a 15526    36  4.6875
36b 15527    62 85.9375
62a 15527    82 32.4564
62b 15528    36 70.3125
82a 15528    62  9.3750
82b 15528    82 74.6875

You can split by the NROW of dat.a if you want.

-- 
David.
 >
> data frame: class62
> 15527	62	85.9375
>
> data frame: class62a
> 15528	62	9.375
>
> data frame: class82
> 15528	82	74.6875
>
> data frame: class82a
> 15527	82	32.4564
>
> Thank you very much your help..
> P.
>
>
>
> --
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>
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David Winsemius, MD
Alameda, CA, USA