R plotly how to use add_trace() to a plot with color grouping

Question

How can I get the following code to draw a line between (1,2) and (3,2)?

plot_ly(x=c(1,2,3),
        y=c(1,2,3),
        type='scatter',
        mode='markers',
        color=as.factor(c('a','b','c')))%>%
  add_trace(x=c(1,3,NA),
            y=c(2,2,NA),
            mode='lines')

The solution here R plotly add_trace to a chart with color groups doesn't work. Thanks.

Edit: Using inherit=FALSE does the job (thanks Jonny Phelps)

plot_ly(x=c(1,2,3),
        y=c(1,2,3),
        type='scatter',
        mode='markers',
        color=as.factor(c('a','b','c')))%>%
  add_trace(x=c(1,3),
            y=c(2,2),
            mode='lines',
            inherit = FALSE,
            line=list(color='black'))

Answer 1

Answering from your comment. I have some real pain with Plotly sometimes. This sort of works, but the legend is a mess, and will need some work.

The challenge is making multiple coloured lines from one series. I don't think Plotly handles these natively (would love to see a better example). Therefore I've just looped it. You might be able to get something more elegant with the group= option.

I added a 4th value in as it shows output better.

edit: I have a real pain point with the colour of "a". If you look at the first p, it is green. After the loop, it becomes brown. That's why I added "lines+markers", instead of "markers". Someone will know how to improve this, but its another Plotly pain

library(plotly)
library(RColorBrewer)

dat <- data.frame(x1=c(1,2,3,4), y1=c(1,2,3,4), mycolor=c('a','b','c','d'), 
                  x2=c(1,2,3,NA), y2=c(1,2,3,NA),
                  stringsAsFactors = FALSE) 
colours <- brewer.pal(length(unique(dat$mycolor)), "Dark2")
p <- plot_ly(data=dat, x=~x1, y=~y1, colors=colours) %>%
   add_trace(mode='markers', color=~mycolor, data=dat, 
             x=~x1, y=~y1) 
p

N <- nrow(dat)-1
for(i in 1:N){
  p <- p %>% add_trace(data=dat[i:(i+1),], x=~x2, y=~y2, mode='lines+markers',
                       type="scatter", color=colours[i],
                       inherit=FALSE) 
}
p