how to force map zero to white color in R plotly color scale

Question

My code is the following but I would like to have white color mapped to 0 instead of the middle values of the max and min of data_bydate$avg_score

g <- plot_ly(data_bydate, x = ~Date, y = ~avg_score, color =data_bydate$avg_score, colors = c("#FF0000","#FFFFFF", "#008000"), mode ='markers', marker = list(size=3)) %>%
layout(legend = list(orientation = 'h'), 
       xaxis = list(title = "",
                    zeroline = FALSE,
                    tickformat="%X",
                    showline = TRUE), 
       yaxis = list(title = "",
                    zeroline = FALSE,
                    showline = TRUE ))

Right now it doesn't give a graph where the above zero values are green and below zero values are red...

Answer 1

You could create your own colorscale which goes from red (min) to white (zero) to greenish (max). The colorscale is a list of arrays which is composed of two separate colorscales, one for the part below zero, from red to white, and the other one above, from white to green.

library(plotly)
library(scales)

set.seed(42)
colorlength <- 100

data_bydate <- data.frame(Date = c(1:23),
                          avg_score = c(runif(10, -5, -1), 
                                        rep(0,3), 
                                        runif(10, 1, 10)
                                        )
                          )

null_value <- (0 - min(data_bydate$avg_score)) / (max(data_bydate$avg_score) - min(data_bydate$avg_score))        
border <- as.integer(null_value * colorlength)
colorscale <- as.list(1:colorlength)

#colorscale below zero
s <- scales::seq_gradient_pal("#FF0000", "#FFFFFF", "Lab")(seq(0,1,length.out=border))
for (i in 1:border) {
    colorscale[[i]] <- c((i - 1) / colorlength, s[i])
}

#colorscale above zero
s <- scales::seq_gradient_pal("#FFFFFF", "#008000", "Lab")(seq(0,1,length.out=colorlength - border))
for (i in 1:(colorlength - border)) {
  colorscale[[i + border]] <- c((i + border) / colorlength, s[i])
}

plot_ly(data_bydate, 
        x = ~Date, 
        y = ~avg_score, 
        type = 'scatter',
        mode ='markers', 
        marker = list(size = 10,
                      color = ~avg_score,
                      colorscale = colorscale,
                      colorbar = list(len=1))) %>%
  layout(plot_bgcolor = 'black')