[R] bar plot stacked

[message]

Readers,

For data set:

a, 90, 10
b, 60, 40
c, ,
d, , 50

A plot was attempted:

dataset<-as.matrix(read.csv("datafile.csv",header=FALSE))
barplot<-(dataset,horiz=TRUE)

A warning message is returned, about NAs introduced by coercion and an 
undesirable graph. The desired output is something similar to:

a	---------*
b	------****
c
d	****

Whereby a legend would be produced to describe '*' and '-'. Any help 
please?