How to change the origin of a barplot?

Question

I have a 2 data set with negative values, so the barplot gives me a plot with bars down. How to set the origin of the y axis in a negative value, in order to obtain bars up?

What I have:

A <- c(-7.3, -2.17, 1.05)
B <- c(-3.69, -5.04, -0.746)
AB <- c(A, B)

barplot(AB, col = c("darkgray","darkgray","darkgray","lightgray","lightgray","lightgray"),#
  names.arg=c("A1", "A2", "A3", "B1", "B2", "B3"))
 legend("bottomright", legend = c("A", "B"), fill = c("darkgray", "lightgray"), horiz = T)

What I want:

Answer 1

new <- abs(-8 - AB)

barplot(new, beside=TRUE, ylim=c(0, 12), yaxt="n",
    col = c("darkgray","darkgray","darkgray","lightgray","lightgray","lightgray"),#
    names.arg=c("A1", "A2", "A3", "B1", "B2", "B3"))

axis(2, seq(0, 12, 2), labels=seq(-8,4,2))
box(bty="l")
legend("topright", legend = c("A", "B"), fill = c("darkgray", "lightgray"), horiz = T)