On Tue, 27 May 2008, T.D.Rudolph wrote:
I have a matrix of frequency counts from 0-160.
x<-as.matrix(c(0,1,0,0,1,0,0,0,1,0,0,0,0,1))
I would like to apply a function creating a new column (x[,2])containing
values equal to:
a) log(x[m,1]) if x[m,1] > 0; and
b) for all x[m,1]= 0, log(next x[m,1] > 0 / count of preceding zero values
+1)
for example, x[1,2] should equal log(x[2,1]/2) = log(1/2) = -0.6931472
whereas x[3,2] should equal log(x[5,1]/3) = log (1/3) = -1.098612
If you also intend that x[4,2] == x[3,2] in your example, then this seems
what you want:
rle.x <- rle(x[,1])
num <- ifelse(rle.x$values == 0, c(tail(rle.x$values,-1),NA), rle.x$values )
denom <- ifelse(rle.x$values == 0 , rle.x$lengths +1 , 1 )
rep(log(num/denom),rle.x$lengths)
[1] -0.6931472 0.0000000 -1.0986123 -1.0986123 0.0000000 -1.3862944
-1.3862944 -1.3862944 0.0000000 -1.6094379
[11] -1.6094379 -1.6094379 -1.6094379 0.0000000
See
?rep
?rle
?tail
HTH,
Chuck
I will be applying this to nrow(x)=~70,000 so I would prefer to not do it by
hand!
Tyler
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
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