library(plotly)

set.seed(11)

# initialize a 5-record data.table with 4 random normal series
df <- data.frame(date = c("1980", "1981", "1982", "1983", "1984"),
                 var1 = rnorm(5), var2 = 10 * rnorm(5), var3 = rnorm(5), 
                 var4 = 10 * rnorm(5))

# plot var1 & var2 on the same plot, different axes
p1 <- plot_ly(df, type = 'scatter', mode = 'lines') %>%
        add_trace(x = ~date, y = ~var1, name = "var1") %>%
        add_trace(x = ~date, y = ~var2, name = "var2", yaxis = "y2") %>%
        layout(yaxis2 = list(side = "right", overlaying = "y", zeroline = FALSE))
p1

# plot var3 & var4 on the same plot, same axis
p2 <- plot_ly(df, type = 'scatter', mode = 'lines') %>%
        add_trace(x = ~date, y = ~var3, name = "var3") %>%
        add_trace(x = ~date, y = ~var4, name = "var4") 
p2

# stack plots p1 & p2
plots <- subplot(p1, p2, nrows = 2, shareY = F, shareX = F)
plots