[R] a problem: factors, names, tables ..

[Uwe Ligges]

PvR wrote:
> Hi all,
> 
> I am *completely* lost in trying to solve a relatively simple task.
> 
> I want to compute the relative number of occurences of an event, the 
> data  of which sits in a large table (read from file).
> 
> I have the occurences of the events in a table 'tt'
> 
> 0  2 10 11 13 14 15
> 15  6  1  3  8 15 10
> 
> .. meaning that event of type '0' occurs 15 times, type '2' occurs 6 
> times  etc.
> 
> Now I want to divide the occurence counts by the total number of events 
> of  that type, which is given in the table tt2:
> 
>  0   1   2  10  11  12  13  14  15
> 817 119 524  96 700  66 559 358 283
> 
> Saying that event type '0' occurred 817 times, type '1' occurs 119 
> times  etc.
> 
> The obvious problem is that not all events in tt2 are present in tt, 
> which  is the result of the experiment so that cannot be changed.
> 
> What needs to be done is loop over tt, take the occurence count, and  
> divide that with the corresponding count in tt2.  This corresponding 
> tt2  count is *not* at the same index in tt2, so I need a reverse lookup 
> of the  type number.  For example:
> 
> event type 10:
> occurs 1 time (from table tt)
> occurs 96 times in total (from table tt2)  <- this is found by looking 
> up  type '10' in tt2 and reading out 96
> 
> result: 1/96
> 
> 
> 
> I have tried programming this as follows:


It's *much* easier. Just make V32 a factor. After that, table() knows 
all the levels and counts also the zeros:

V32 <- factor(V32)
table(V32[V48 == 0]) / table(V32)

Uwe Ligges




> 
> tt <- table(V32[V48 == 0]) # this is taking the events I want counted
> tt2 <- table(V32) # this is taking the total event count per type
> df <- as.data.frame(tt) #convert to dataframe to allow access to  
> type-numbers .. ?
> df2 <-  as.data.frame(tt2) #same here
> 
> print(tt);
> print(df);
> 
> print(tt2);
> print(df2);
> 
> for( i in 1:length(tt) ) { #loop over smallest table tt
>     print("i:"); #index
>     print(i);
>     print( "denominator "); #corresponds to the "1" in the example
>     print(     df$Freq[i] );
>     denomtag = ( df$Var1[ i ] );    # corresponds to the "10" in the 
> example,  being the type number of the event
>     print("denomtag ");
>     print( denomtag );
>     print( "nominator: " );
>     print( df2[2][ df[1] == as.numeric(denomtag) ] );  #this fails ....
>     #result would then be somthing like :  denomitor / nominator   
> }
> 
> The problem is that the factor names that are extracted in 'denomtag' 
> are  not usable as index in the dataframe in the last line.   I have 
> tried  converting to numeric using 'as.numeric', but that fails since 
> this  returns the index in the factor rather then the factor name I need 
> from  the list.
> 
> Any suggestions .. ?   I am sure its dead simple, as always.
> 
> 
> Thanks,
> 
> 
> Piet (Belgium)
> 
> PS: please reply to pvremortNOSPAM at vub.ac.be
> 
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