A. Mani : Tapply

Hi

PLEASE do read the posting guide! 

******************************

Hello, 
        Is it safe to use tapply when the result will be of dim 20000 
x 10000 or more ? In my PC R crashes.  

or gave you an error message? 

I tried this

df<-data.frame(A=as.factor(sample(1:10000,100000,  

replace=T)),B=as.factor(sample(100000:110000,100000,  
replace=T)), num=rnorm(100000))

ttt<-tapply(df$num, list(df$A,df$B), diff) 

and got 

Error: cannot allocate vector of size 390664 Kb 
In addition: Warning messages: 
1: Reached total allocation of 1000Mb: see help(memory.size)  
2: Reached total allocation of 1000Mb: see help(memory.size)

and the result with smaller data sets are 

df1<-data.frame(A=as.factor(sample(1:2,100000, 
replace=T)),B=as.factor(sample(10:11,100000, replace=T)), 
num=rnorm(100000)) 
ttt1<-tapply(df1$num, list(df1$A,df1$B), diff)

ttt1 

10            11            
1 Numeric,24933 Numeric,25141 
2 Numeric,24992 Numeric,24930 


df<-data.frame(A=as.factor(sample(1:1000,100000, 
replace=T)),B=as.factor(sample(10000:11000,100000, 
replace=T)), num=rnorm(100000)) 
 ttt<-tapply(df$num, list(df$A,df$B), diff)

ttt[1:2,1:5] 

10000 10001 10002 10003     10004 
1 NULL  NULL  NULL  Numeric,0 NULL  
2 NULL  NULL  NULL  Numeric,0 NULL

so you are probably receiving humonguous table of NULLs, zeros  
and few nonzero entries. 

You probably need to use different approach 

Cheers 
Petr 


The code used was on a 3-col

data frame with two factor cols and a numeric column. The fn 

was diff

. data form being <A, B, Num> tapply(data$A, list(data$A, 

data$B),

diff) 
 
--  
A. Mani 
Member, Cal. Math. Soc 
 

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Petr Pikal
petr.pikal at precheza.cz