Make base of bars configurable

[etpinard]

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?

[mdtusz]

To clarify, do you mean so that all negative values stack below and all positive values stack above?

[etpinard]

To clarify, do you mean so that all negative values stack below and all positive values stack above?

Yes. That's what I'm thinking.

[etpinard]

Maybe we should also generalize the base level of the bars. Right now, positive values span above the zero line and negative values below it, but what if a user wants to plot bars on each side of y=20 ?

[mdtusz]

Maybe barmode: 'relative' with some specification for the base value?

{
  barmode: 'relative',
  barbase: 42
}

I don't like barbase though. @cldougl ?

[mdtusz]

And we could use barbase for the other modes too now that I think of it.

[keeganmccallum]

#517, didn't setup a 'barbase' type functionality, but properly provides a 'relative' barmode that behaves as described.

[etpinard]

'relative' bar mode added in #517

Issue title changed to reflect barbase feature.

[programflex]

[http://codepen.io/etpinard/pen/mPGLrY] It seems 'relative' does not work if the first index of y in trace2 is a negative value and the first index of y in trace1 is a positive value.
Like this:
var trace1 = {
x: ['giraffes', 'orangutans', 'monkeys'],
y: [20, 14, -23],
name: 'SF Zoo',
type: 'bar'
};
var trace2 = {
x: ['giraffes', 'orangutans', 'monkeys'],
y: [-12, -18, 29],
name: 'LA Zoo',
type: 'bar'
};

[etpinard]

@programflex thanks for reporting ➡️ #639

[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")