R | ECharts | area bands (confidence bands)

area.bands.R

#'  Area band (confidence bands) is a 'custom' serie with lower and upper boundaries   
#'  When type='polygon', coordinates of the two boundaries are chained into a polygon and displayed as one.
#'  When type='stack', two (smooth) stacked lines are drawn, one with customizable areaStyle. 
#'       The upper boundary coordinates should be values added on top of the lower boundary coordinates.
#'  Standard and custom(formatter) tooltips could be used.
#'
#' ec.init(load='custom') will preset values like dataset, xAxis, etc.
#' those could be customized (like xAxis below), and new ones added - like legend and tooltip.

library(echarty)

set.seed(5)
df <- data.frame( x = 1:10, y = runif(10, 5, 10)) %>%
  dplyr::mutate(lwr = y-runif(10, 1, 3), upr = y+runif(10, 2, 4))

# --------- type='stack'
p <- df %>% ec.init(load='custom')
p$x$opts$xAxis <- list(type='category', boundaryGap=FALSE)
p$x$opts$series <- append( list(list(type='line', color='gold', name='line1')),
          ecr.band(df, 'lwr', 'upr', type='stack', name='stak') #, smooth=FALSE)
)
p$x$opts$tooltip <- list(trigger = 'axis'
                         ,formatter = htmlwidgets::JS("function(x) {
  let str = x.length>1 
  ? 'high <b>'+x[2].value[2]+'</b><br>line <b>'+x[0].value[1]+'</b><br>low <b>'+x[1].value[1]+'</b>' 
  : 'line <b>'+x[0].value[1]+'</b>';
  return str;  }"))
p$x$opts$legend <- list(ii='')
p

# --------- type='polygon'
p <- df %>% ec.init(load='custom')
p$x$opts$xAxis <- list(type='category', boundaryGap=FALSE)
p$x$opts$series <- append( list(list(type='line', color='gold', name='line1')),
          ecr.band(df, 'lwr', 'upr', type='polygon', name='poly')
)
p$x$opts$tooltip <- list(trigger = 'axis')
p$x$opts$legend <- list(ii='')
p

Works great! Thank you!