[R] Odp: Problem in converting natural numbers to bits and others

[Petr PIKAL]

Hallo

r-help-bounces at r-project.org napsal dne 21.05.2008 09:42:40:

> Hi,
> 
> I just started using R for about one week and I have few problems.
> 
> i)I have a problem in finding right function to convert a table of 
natural
> numbers to bitwise. For a simple example;
> 
> I have the below table:-
> 
> Column  Col1   Col2   Col3
> Sample1 5        7      10
> Sample2 0        2       1
> Sample3 4         0       0
> 
> 
> Supposedly i wanted to convert to :-
> 
> 
> Column  Col1   Col2   Col3
> Sample1 1        1       1
> Sample2 0        1       1
> Sample3 1         0       0

data<-read.table("clipboard", header=T
If data is your data frame, 

data.bit<-data.frame(column=data[,1],(data[,-1]>0)*1)

> 
> ii)Besides, I would like to create a formula of Sum(3*(Element in each
> column for a row))..does it equivalent to 3*(data[1:3,1:2]) in this 
case?or
> I need to have Sum(3*(data[1:3,1:2])). Basically I wanted to mutliply 
each
> element of column table of a row and sum it  up.

Rather complicated. 

> 3*(data[1:3,2:3])
  Col1 Col2
1   15   21
2    0    6
3   12    0
> sum(3*(data[1:3,2:3]))
[1] 54

Works but I am suspicious that you wont something else. 


> 
> iii)I would also like to know how to insert an if else statement where 
in
> the above case, I wanted to check if data[1:3,]
> returns me 1 or 0, it will execute some calculations.
> I refer to the R intro pdf and it mentioned using if (expr_1 ) expr_2 
else
> expr_3. Does that mean if(data[1:3,1:2])>0 output[1:3,1:2]=0
> else output[1:3,1:2]="100". If I did this command, how does R knows 
which
> row and column to map the output with?

If ... else ... is usually for working as programming steps

ifelse(..., ..., ...)

works with objects and is parts. You shall think first how to do your 
calculations with whole objects, it is usually more effective.

Regards
Petr

> 
> Please advise. Appreciate alot. Thanks.
> 
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> 
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