[R] a problem: factors, names, tables ..
Adaikalavan Ramasamy
ramasamy at cancer.org.uk
Sun Jul 18 16:19:14 CEST 2004
Please give a reproducible example. Here is one way :
# generate example
> v1 <- rep( c(0, 2, 10, 11, 13, 14, 15), c(15, 6, 1, 3, 8, 15, 10) )
> t1 <- table(v1)
> t1
v1
0 2 10 11 13 14 15
15 6 1 3 8 15 10
> v2 <- rep( c(0, 1, 2, 10, 11, 12, 13, 14, 15), c(817, 119, 524, 96,
700, 66, 559, 358, 283) )
> t2 <- table(v2)
> t2
v2
0 1 2 10 11 12 13 14 15
817 119 524 96 700 66 559 358 283
# find results
> merge(t1, t2, by=1, all.x=TRUE)
v1 Freq.x Freq.y
1 0 15 817
2 10 1 96
3 11 3 700
4 13 8 559
5 14 15 358
6 15 10 283
7 2 6 524
Uwe's suggestion may need a slight modification as the two table have
different labels/levels and hence non-conformable for division
> t2.f <- table( v2.f <- factor(v2) )
> t1.f <- table( v1.f <- factor(v1, levels=levels(v2.f)) )
> cbind( t1.f, t2.f, ratio=t1.f / t2.f )
t1.f t2.f ratio
0 15 817 0.018359853
1 0 119 0.000000000
2 6 524 0.011450382
10 1 96 0.010416667
11 3 700 0.004285714
12 0 66 0.000000000
13 8 559 0.014311270
14 15 358 0.041899441
15 10 283 0.035335689
>
Also have a look at this related posting
http://tolstoy.newcastle.edu.au/R/help/04/06/0594.html
Regards, Adai.
On Sun, 2004-07-18 at 13:05, Uwe Ligges wrote:
> 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
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
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> > PLEASE do read the posting guide!
> > http://www.R-project.org/posting-guide.html
>
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