Customize hover text for plotly heatmap

Question

I have a matrix (gene expression from several conditions):

set.seed(1)
mat <- matrix(rnorm(50*10),nrow=50,ncol=10,dimnames=list(paste("C",1:50,sep="."),paste("G",1:10,sep=".")))

Which I want to plot as a heatmap using plotly in R.

require(plotly)
heatmap.plotly <- plot_ly(x=colnames(mat),y=rownames(mat),z=mat,type="heatmap",colors=colorRamp(c("darkblue","white","darkred")),colorbar=list(title="Score",len=0.4)) %>%
  layout(yaxis=list(title="Condition"),xaxis=list(title="Gene"))

works fine.

However, I'd like to add text that would be seen only when hovered over.

I thought this would work:

conditions.text <- paste(paste("C",1:50,sep="."),rep(paste(LETTERS[sample(26,10,replace=T)],collapse=""),50),sep=":")
heatmap.plotly <- plot_ly(x=colnames(mat),y=rownames(mat),z=mat,type="heatmap",colors=colorRamp(c("darkblue","white","darkred")),colorbar=list(title="Score",len=0.4),hoverinfo='text',text=~conditions.text) %>%
  layout(yaxis=list(title="Condition"),xaxis=list(title="Gene"))

But it doesn't. I actually don't see any text when hovering over the plot.

Note that I'm working with a matrix rather than a melted data.frame.

Answer 1

You are passing an array of 50x10 into your heatmap but a list of 50 entries as hoverinfo. Both the input for the heatmap and the text must have the same dimensions.

library(plotly)
set.seed(1)
mat <- matrix(rnorm(50*10),nrow=50,ncol=10,dimnames=list(paste("C",1:50,sep="."),paste("G",1:10,sep=".")))

conditions.text <- paste(paste("C",1:50,sep="."),rep(paste(LETTERS[sample(26,10,replace=T)],collapse=""),500),sep=":")
conditions.text <- matrix(unlist(conditions.text), ncol = 10, byrow = TRUE)

plot_ly(z=mat,
        type="heatmap",
        hoverinfo='text',
        text=conditions.text)