R Plotly set custom colors for bar chart

Question

I've got a plotly bar chart in my Shiny app, and I'd like to set specific colors each column in the resulting bar chart.

#Here's some reproducible data
df=data.frame(Month=c("Jan","Feb","Mar","Apr","May","Jun"),Criteria1=c(10,15,20,15,7,6),Criteria2=c(3,8,5,7,9,10),Criteria3=c(11,18,14,9,3,1))

#Plot

colNames <- names(df)[-1] #Month is the first column

# Here is where I set the colors for each `Criteria`, assuming that the order of colors follows the same order as the factor levels of the `Criteria`.

p <- plotly::plot_ly(marker=list(colors=c('#CC1480', '#FF9673', '#E1C8B4')))

for(trace in colNames){
  p <- p %>% plotly::add_trace(data = df, x = ~Month, y = as.formula(paste0("~`", trace, "`")), name = trace, type = "bar")
}

p %>% 
  layout(title = "Trend Over Time",showlegend = FALSE,
         xaxis = list(title = ""),
         yaxis = list (title = "Monthly Count of QoL Tweets"))

However the resulting plot does not show any of the colors I specify.

What am I doing incorrectly? Any pointers would be very appreciated.

Answer 1

I don't think loop is neccessary here, the following provides as well more control over choosing the color for specific levels when df is melted, the individual levels Criteria1, Criteria2, Criteria3

library(plotly)
library(reshape2)

#Yout data.frame
df <- data.frame(Month = c("Jan","Feb","Mar","Apr","May","Jun"),
                 Criteria1 = c(10,15,20,15,7,6),
                 Criteria2 = c(3,8,5,7,9,10),
                 Criteria3 = c(11,18,14,9,3,1))

melt(df, id.vars = 'Month') %>% plot_ly(x = ~Month, y = ~value, type = 'bar', 
  color = ~variable,
  colors = c(Criteria1 = '#CC1480', Criteria2 = '#FF9673', Criteria3 = '#E1C8B4'))

Answer 2

You could assign your colors to a vector:

colors <- c('#CC1480', '#FF9673', '#E1C8B4')

and then add the traces in a slightly modified loop.

p <- plotly::add_trace(p, 
                       x = df$Month, 
                       y = df[,trace], 
                       marker = list(color = colors[[match(trace, colNames)]]), 
                       name = trace, 
                       type = "bar")
}

which will give you the following graph

Complete code

library("plotly")
df=data.frame(Month=c("Jan", "Feb","Mar", "Apr", "May", "Jun"),
              Criteria1 = c(10, 15,20,15,7,6),
              Criteria2 = c(3, 8, 5, 7, 9, 10),
              Criteria3 = c(11, 18, 14, 9, 3, 1))

colNames <- names(df)[-1] #Month is the first column
colors <- c('#CC1480', '#FF9673', '#E1C8B4')
p <- plotly::plot_ly()

#colNames = c('Criteria1')
for(trace in colNames){
  p <- plotly::add_trace(p, 
                         x = df$Month, 
                         y = df[,trace], 
                         marker = list(color = colors[[match(trace, colNames)]]), 
                         name = trace, 
                         type = "bar")
}

p