[R] operation with if/else on a dataframe

[Bernardo Rangel Tura]

On Thu, 2009-10-29 at 01:47 -0700, Fran100681 wrote:
> Hi to all,
> I have this dataframe (I show the first six rows)
> 
> >head(table)
> 
>  A                                           R    Fold.Change     P.Value 
> Count1   Count2        
> 1 ENSRNOE00000000002_at         0         1.13             0.60        1      
> 1
> 2 ENSRNOE00000000009_at         0        -1.04             0.73        3      
> 3
> 3 ENSRNOE00000000020_at         0        -1.08             0.68        0      
> 0
> 4 ENSRNOE00000000021_at         0        -1.31             0.20        1      
> 2
> 5 ENSRNOE00000000023_at         0        -1.06             0.64        3      
> 3
> 6 ENSRNOE00000000024_at         0        -1.14             0.40        3      
> 3
> 
> I would like to generate a function that determine for each row a new value
> (resulting in a new vector of values to add to the dataframe). 
> The function should give for every row the same value showed in column "R".
> However,I need of this because not all the R-values reported in this table
> are correctly determined following the criteria mentioned below.
> 
> 
> These new values calculated by the function must be:
> 
> 1)"UP" 
> if all the following conditions are verified in a certain row:
> Fold.Change is >= +1.5, 
> P.Value is < 0.05 
> Count1 >= 2
> 
> 2)"DOWN"
> if all the following conditions are verified in a certain row:
> Fold.Change is <= -1.5, 
> P.Value is < 0.05 
> Count2 >= 2
> 
> 3) 0 if both of previous conditions are not verified
> 
> So I have set these fllowing parameters (new objects) because I'll have to
> repeat this procedure to different dataframes in which the order of columns
> of interest might change (So I can change these parameters depending on the
> order of the columns in any different table)
> 
> Fold.change <-  3 #(because in this table, Fold.Change value is the third
> column and so on...)
> P.Value <-  4
> Count1 <-  5
> Count2 <-  6

[ Quote text]

> This is my problem, I cannot use the function to recalculate values in
> R-column for all rows in my dataframe. I don't understand  where is the
> problem, can someone help me?
> Thanks a lot!!
> 
> Francesco

Francesco,


I think you solve this problem with a simple way.
Remember in R the most function and operations are vectorized so look
this example: 

set.seed(123)
x<-rpois(20,5)
y<-rpois(20,15)
z<-rpois(20,10)
dta<-data.frame(x,y,z)
dta
dta$NEW<-ifelse(x>5 & y>15 & z>10,"UP",
ifelse(x<5 & y<15 & z<10,"DOWN",
"0"))
dta

First, I use ifelse command to simplify your nested conditional
situation.

Second, I know that R test this nested condition in order so the first
position will result test x[1],y[1] and z[1], the second postion will
result test x[2],y[2] and z[2] ...

The new vector result is the same order the original data.frame so I use
dta$NEW to create a new column in data.frame 



-- 
Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
Brazil