full code for the improved correlation plot

improvedCorrelationPlot.R

library(plotly)
library(data.table)

data <- mtcars[,c(1,3:7)]
corrdata <- cor(data)


#do this before the transformation!
corrdata[upper.tri(corrdata, diag = TRUE)] <- NA
corrdata <- corrdata[-1, -ncol(corrdata)]

#Store our variable names for later use
x_labels <- colnames(corrdata)
y_labels <- rownames(corrdata)

#Change the variable names to numeric for the grid
colnames(corrdata) <- 1:ncol(corrdata)
rownames(corrdata) <- nrow(corrdata):1

#Melt the data into the desired format
plotdata <- melt(corrdata)

#Adding the size variable & scaling it
plotdata$size <- (abs(plotdata$value))
scaling <- 500 / ncol(corrdata) / 2
plotdata$size <- plotdata$size * scaling

#Setting x and y ranges for the chart
xrange <- c(0.5, length(x_labels)+0.5)
yrange <- c(0.5, length(y_labels)+0.5)

#Setting the gridlines
x_grid <- seq(1.5, length(x_labels)-0.5, 1)
y_grid <- seq(1.5, length(y_labels)-0.5, 1)

#Axes definitions
xAx1 <- list(showgrid = FALSE,
            showline = FALSE,
            zeroline =  FALSE,
            tickvals = colnames(corrdata),
            ticktext = x_labels,
            title = "",
            range = xrange,
            rangemode = "tozero")

xAx2 <- list(showgrid = TRUE,
            showline = FALSE,
            zeroline =  FALSE,
            overlaying = "x",
            showticklabels = FALSE,
            range = xrange,
            tickvals = x_grid)

yAx1 <- list(autoaxis = FALSE,
            showgrid = FALSE,
            showline = FALSE,
            zeroline =  FALSE,
            tickvals = rownames(corrdata),
            ticktext = y_labels,
            title = FALSE,
            rangemode = "tozero",
            range = yrange)

yAx2 <- list(showgrid = TRUE,
            showline = FALSE,
            zeroline =  FALSE,
            overlaying = "y",
            showticklabels = FALSE,
            range = yrange,
            tickvals = y_grid)


fig <- plot_ly(data = plotdata, width = 500, height = 500)
fig <- fig %>% add_trace(x = ~Var2, y = ~Var1, type = "scatter", mode = "markers",
                        color = ~value,
                        marker = list(size = ~size, opacity = 1),
                        symbol = I("square"),
                        text = ~value,
                        hovertemplate = "%{text:.2f} <extra></extra>",
                        xaxis = "x1",
                        yaxis = "y1")

fig <- fig %>% add_trace(x = ~Var2, y = ~Var1, type = "scatter", mode = "markers",
                        opacity = 0,
                        showlegend = FALSE,
                        xaxis = "x2",
                        yaxis = "y2",
                        hoverinfo = "none")

fig <- fig %>% layout(xaxis = xAx1,
                     yaxis = yAx1, 
                     xaxis2 = xAx2,
                     yaxis2 = yAx2,
                     plot_bgcolor = "rgba(0,0,0,0)",
                     paper_bgcolor = "rgba(0, 0, 0, 0.03)")

fig <- fig %>% colorbar(title = "", limits = c(-1,1), x = 1.1, y = 0.75)