Overlaying two histograms in R Plotly - r

Question

I'm trying to overlay two histogram plots in R plotly. However only one of them shows up. Here's the code I'm using with some random data:
myDF <- cbind.data.frame(Income = sample(1:9, size = 1000, replace= TRUE),
AgeInTwoYearIncrements = sample(seq(from = 2, to = 70, by = 2), size = 1000, replace = TRUE))
plot_ly(data = myDF, alpha = 0.6) %>%
add_histogram(x = ~Income, yaxis = "y1") %>%
add_histogram(x = ~AgeInTwoYearIncrements, yaxis = "y2") %>%
layout(
title = "Salary vs Age",
yaxis = list(
tickfont = list(color = "blue"),
overlaying = "y",
side = "left",
title = "Income"
),
yaxis2 = list(
tickfont = list(color = "red"),
overlaying = "y",
side = "right",
title = "Age"
),
xaxis = list(title = "count")
)
Any help would be much appreciated!

Answer 1

It is the main cause to give the 1st yaxis overlaying. And because xaxis is count, Income and Age is y.
plot_ly(data = myDF, alpha = 0.6) %>%
add_histogram(y = ~Income, yaxis = "y1") %>% # not `x =`
add_histogram(y = ~AgeInTwoYearIncrements, yaxis = "y2") %>%
layout(
title = "Salary vs Age",
yaxis = list(
tickfont = list(color = "blue"),
# overlaying = "y", # the main cause is this line.
side = "left",
title = "Income"
),
yaxis2 = list(
tickfont = list(color = "red"),
overlaying = "y",
side = "right",
title = "Age"
),
xaxis = list(title = "count")
)
[Edited: just flip]
plot_ly(data = myDF, alpha = 0.6) %>%
add_histogram(x = ~ Income, xaxis = "x1") %>%
add_histogram(x = ~ AgeInTwoYearIncrements, xaxis = "x2") %>%
layout(
margin = list(t = 60),
title = "Salary vs Age",
xaxis = list(
tickfont = list(color = "blue"),
side = "left",
title = "Income"
),
xaxis2 = list(
tickfont = list(color = "red"),
overlaying = "x",
side = "top",
position = 0.95,
title = "<br>Age"
),
yaxis = list(title = "count")
)

Answer 2

You can mix histograms:
plot_ly(data = myDF, alpha = 0.6) %>%
add_histogram(x = ~Income) %>%
add_histogram(x = ~AgeInTwoYearIncrements) %>%
layout(
title = "Salary and Age",
yaxis = list(
tickfont = list(color = "blue"),
overlaying = "y",
side = "left",
title = "count"
),
xaxis = list(title = "Salary and Age value")
)
A histogram has normally on the y-axis the frequency / count and not on the x-axis. We can produce a diagram like you want but I'm not sure if it is still a histogram.
Also, like you see in my picture you the frequency/count for salary (here blue) is more high and the variability is less then age. That make it difficult for a good looking diagram. Maybe this is just a problem of your sample data...
So When you like to go with the histogram function, you have to invert the meaning of the frequency and the value on the x-axis.
But anyway, I think a scaternplot would be a better solution to show the relation between salary and age.
edit:
This is the result I get when I run your code:
Like this I don't see the sense in the plot and what you want. The meaning of the first orange colum is that a age of 59 occurs between 0 and 5 times in your dataset. The third colum means a age of 88 ocours between 10 and 15 times in your dataset.
To present this information in a barplot don't work. Because you can have several Age-values in on categorie of counts...I hope this is clear.
Anyway, to answer your question I need more clarification.

Answer 3

Following the responses here, I wanted to answer this with an example that others can easily use when for instance plotting two overlapping histograms.
# Add required packages
library(plotly)
# Make some sample data
a = rnorm(1000,4)
b = rnorm(1000,6)
# Make your histogram plot with binsize set automatically
fig <- plot_ly(alpha = 0.6) # don't need "nbinsx = 30"
fig <- fig %>% add_histogram(a, name = "first")
fig <- fig %>% add_histogram(b, name = "second")
fig <- fig %>% layout(barmode = "overlay",
yaxis = list(title = "Frequency"),
xaxis = list(title = "Values"))
# Print your histogram
fig
And here is the result of the code:

Answer 4

Easy way to handle any number of dimensions without repetition
TL;DR: You can rearrange your data to long-form before passing it to plot_ly().
df |>
mutate(row_number = row_number()) |>
pivot_longer(!row_number) |>
plot_ly() |>
add_histogram(x = ~ value,
color = ~ name,
opacity = 0.5) |>
layout(barmode = 'overlay')
Explanation
Given a DF with multiple columns, like the one the OP posted:
df = cbind.data.frame(Income = sample(1:9, size = 1000, replace= TRUE),
AgeInTwoYearIncrements = sample(seq(from = 2, to = 70, by = 2), size = 1000, replace = TRUE))
Then, using tidyr::pivot_longer():
df |> mutate(row_number = row_number()) |> pivot_longer(!row_number)
This gives:
# A tibble: 2,000 × 3
row_number name value
<int> <chr> <dbl>
1 1 Income 1
2 1 AgeInTwoYearIncrements 20
3 2 Income 1
4 2 AgeInTwoYearIncrements 48
5 3 Income 3
6 3 AgeInTwoYearIncrements 26
7 4 Income 4
8 4 AgeInTwoYearIncrements 30
9 5 Income 4
10 5 AgeInTwoYearIncrements 60
# … with 1,990 more rows
Finally, just pipe this to plot_ly(), so the full command is:
df |>
# Add a column to keep track of the row numbers
mutate(row_number = row_number()) |>
# Squash and lengthen the df with one row per row per column (in this case, double its length)
pivot_longer(!row_number) |>
plot_ly() |>
# The magic is here. We set color to track the name variable, which will
# add a separate series per column.
# We set the opacity so we can see where our plots overlap.
add_histogram(x = ~ value,
color = ~ name,
opacity = 0.5) |>
# Without setting this, bars will be plotted side by side for the same x value
# rather than overlapping.
layout(barmode = 'overlay')
Output