On Jul 5, 2009, at 1:19 PM, Uwe Ligges wrote:
snippedpreample
test <- data.frame(A=1:10, B=100, C1=runif(10), C2=runif(10),
C3=runif(10), C4=runif(10), C5=runif(10), C6=runif(10))
test<-round(test,2)
#Make array ragged
test$C3[2]<-0;test$C4[2]<-0;test$C5[2]<-0;test$C6[2]<-0
test$C4[3]<-0;test$C5[3]<-0;test$C6[3]<-0
test$C6[7]<-0
test$C4[8]<-0;test$C5[8]<-0;test$C6[8]<-0
test
#C1 always the same so calculate it only once
StartCol <- which(names(test)=="C1")
#Print row 3 explicitly
test[3,][StartCol :(which(test[3,] == 0.0)[1]-1)]
#Row 6 fails because 0 is not found
test[6,][StartCol :(which(test[6,] == 0.0)[1]-1)]
EndCol <- which(test[6,] == 0.0)[1]-1
EndCol
It's getting a bit Baroque, but here is a solution that handles an
NA:
test[6,][StartCol :ifelse(is.na( which(test[6,] == 0.0)[1]) ,
ncol(test), which(test[6,] == 0.0)
[1]-1 )
]
#####-----
C1 C2 C3 C4 C5 C6
6 0.33 0.84 0.51 0.86 0.84 0.15
Maybe an R-meister can offer something more compact?
So let's wait for some R-meister, I'd write even more ....
Reason: testing for exactly zero after possible calculations is a
bit dangerous and ifelse() is designed for vectorized operations but
is not efficient for scalar operations, particularly since both
expressions are evaluated, so if() else would be preferable, but we
could use min() instead. Finally, a:b could end up in 5:3 without a
warning and I'd use seq() instead.
Hence I'd prefer:
temp <- which(sapply(test[6,], function(x, y)
isTRUE(all.equal(x,y)), 0))[1]
This appears to be learning moment for me. Do I have it correctly that
the first argument to sapply, the vector(test[6,], gets passed
element-wise to the first parameter of the function, x, and the second
argument, 0, is getting passed via recycling to the second parameter,
y, through the , ...) mechanism of the sapply function?
test[6, seq(from = StartCol, to = min(c(temp - 1, ncol(test)), na.rm
= TRUE), by = 1)]
I had tried a min() solution and got Inf in return when there was an
NA in the vector, but did not realize that it had an na.rm mode.
Thanks for the meisterhaft corrections.
Best,
Uwe Ligges
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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