Plotting add_trace from within a function: Plotly

Question

I am trying to "functionize" my plot statements. If i want to add an additional trace from another dataframe, i am getting an error that the values on the y axis do not equal the first number of values in the first dataframe. I am not certain why this is relevant.

library(tidyverse)
library(plotly) 
library(lubridate)

Date <- seq(as.Date("2016-10-1"), as.Date("2018-09-01"), by="month")
Values <- c(2,3,4,3,4,5,6,4,5,6,7,8,9,10,8,9,10,11,12,13,11,12,13,14)

Date2 <- seq(as.Date("2018-07-1"), as.Date("2018-09-01"), by="month")
Values2 <- c(16,17,18)

df <- tibble::tibble(Date, Values)
df2 <- tibble::tibble(Date2, Values2)



testfunction <- function(x, y, y2){

p <-  plot_ly(df,x = ~x, y = ~y, colors = "Blues", type = 'scatter', mode = 'lines') %>% 
     add_trace(data = df2, y = ~y2, line = list(color = 'rgb(255, 36,1)', width = 2.25)) %>% 
     layout(xaxis = list(tickformat = "%b %e"))

      p  
}

testfunction(Date, Values, Values2)

#Error: Column `y` must be length 1 or 24, not 3

Answer 1

Notice that Date, Values, and Values2 are objects that exist in your global environment. So, testfunction is actually using those objects in the call to plot_ly. To demonstrate this, try removing df in the plot_ly call -- you should still be able to get a plot (i.e. plot_ly isn't actually using the values in the dataframe). However, I suspect what you're trying to do is to specify variable names in your dataframe in the arguments to your function. In which case, try

testfunction <- function(x, y, x2, y2) {
  x <- enquo(x)
  y <- enquo(y)
  x2 <- enquo(x2)
  y2 <- enquo(y2)
  plot_ly(df, x = x, y = y, type = "scatter", mode = "lines") %>%
    add_trace(x = x2, y = y2, data = df2)
}

testfunction(Date, Values, Date2, Values2)

with a hat tip to this question and answer: Pass variables as parameters to plot_ly function