Make base of bars configurable

so that positive and negative values can be stacked on each side of the zero line.

See current behavior of the each barmode here: http://codepen.io/etpinard/pen/mPGLrY?

[kk45991]

Hello, I am using plotly with R and I do not see any difference between: barmode = “relative” and barmode = “group”.

So with the first options values are not stacked like in the example: http://codepen.io/etpinard/pen/mPGLrY

Like this: require(plotly) require(dplyr) set.seed(1) test_data <- data.frame(x = rep(1:10, 3), y = rnorm(30), z = rep(c(“A”, “B”, “C”), 10)) plot_ly(data = test_data, x = x, y = y, color = z, type = “bar”) %>% layout(barmode = “relative”)

plot_ly(data = test_data, x = x, y = y, color = z, type = “bar”) %>% layout(barmode = “group”)

[etpinard]

'relative' bar mode added in https://github.com/plotly/plotly.js/pull/517

Issue title changed to reflect barbase feature.