Secondary axis in plotly does not work for different scales - r

Question

How can I reproduce the following graph in plotly
library(dplyr)
library(ggplot2)
tibble(x =1:10, y = 1:10) %>%
ggplot(aes(x,y)) +
geom_line() +
scale_y_continuous(sec.axis = ~.*2)
I tried the following code based on this answer here
library(dplyr)
library(plotly)
tibble(x =1:10, y = 1:10) %>%
mutate(y2 = y*2) %>%
plot_ly() %>%
add_lines(x =~x, y =~y) %>%
add_lines(x= ~x, y=~y2,
yaxis = "y2", color = I("transparent"),
hoverinfo='skip', showlegend=FALSE) %>%
layout(yaxis2 = list(side = "right", overlaying = "y", showgrid = FALSE),
margin = list(r = 50))
While at first glance it appears to work, it only provides a partial solution, since if I interactively try to change the scale of the main (left) y axis on the produced graph (by dragging it up or down), the right axis does not move with the graph (because it is linked only to the second invisible graph). This of course is not acceptable as it does not allow using any of interactive features of plotly reliably which is the reason I wanted to use it to begin with instead of ggplot.
Edit: Just realized that this plotly solution does not seem to work at all in the case of non linear transformation between the axes (while ggplot handles it beautifully).

Answer 1

You just need to set up dtick and tick0 for plotly to have the same graph as ggplot2 one. See below;
library(plotly)
library(dplyr)
tibble(x =1:10, y = 1:10) %>%
mutate(y2 = y*2) -> df1
n0 <- 4
y0 <- max(df1$y)/n0
x0 <- max(df1$x)/n0
df1 %>%
plot_ly(data = . , x = ~x, y = ~y,
type = "scatter", mode = "lines", width = 800,
color = I("red"), name = "") %>%
add_trace(x = ~x, y = ~y2, yaxis = "y2",
color = I("red"), name = "") %>%
layout(yaxis = list(showline = FALSE, side = "left",
title = "", color = "red",
dtick = y0, tick0 = y0, fixedrange=TRUE),
yaxis2 = list(showline = FALSE, side = "right", overlaying = "y", position = 1,
title = "", anchor = "free", color = "blue",
dtick = 2*y0, tick0 = 2*y0, fixedrange=TRUE),
xaxis = list(showline = FALSE, zeroline = FALSE, title = "",
dtick = x0, tick0 = x0),
showlegend = FALSE,
margin = list(l = 50, r = 50, b = 50, t = 50, pad = 4)
)
Created on 2020-06-19 by the reprex package (v0.3.0)