Add a population_pyramid function

population_pyramid makes a pairwise barchart allow comparison of two variables across a number of observations.
Here's a highcharter example:
pyramid_data <- structure(list(total.projects = c(7.6656596537564, 7.6656596537564, 
7.6656596537564, 7.6656596537564, 7.6656596537564, 7.6656596537564, 
3.74825883246803, 3.74825883246803, 3.74825883246803, 3.74825883246803, 
3.74825883246803, 3.74825883246803, 4.11910490421317, 4.11910490421317, 
4.11910490421317, 4.11910490421317, 4.11910490421317, 4.11910490421317, 
0.827619891821487, 0.827619891821487, 0.827619891821487, 0.827619891821487, 
0.827619891821487, 0.827619891821487, 0.229743663959189, 0.229743663959189, 
0.229743663959189, 0.229743663959189, 0.229743663959189, 0.229743663959189, 
0.0759782195770546, 0.0759782195770546, 0.0759782195770546, 0.0759782195770546, 
0.0759782195770546, 0.0759782195770546, 0.00180900522802511), 
    category = c("Asia", "Asia", "Asia", "Asia", "Asia", "Asia", 
    "Europe", "Europe", "Europe", "Europe", "Europe", "Europe", 
    "North America", "North America", "North America", "North America", 
    "North America", "North America", "Africa", "Africa", "Africa", 
    "Africa", "Africa", "Africa", "South America", "South America", 
    "South America", "South America", "South America", "South America", 
    "Oceania", "Oceania", "Oceania", "Oceania", "Oceania", "Oceania", 
    "Netherlands Antilles"), total.workers = c(8.21693826799704, 
    8.21693826799704, 8.21693826799704, 8.21693826799704, 8.21693826799704, 
    8.21693826799704, 4.59954332874319, 4.59954332874319, 4.59954332874319, 
    4.59954332874319, 4.59954332874319, 4.59954332874319, 2.80143493544363, 
    2.80143493544363, 2.80143493544363, 2.80143493544363, 2.80143493544363, 
    2.80143493544363, 0.639043820279792, 0.639043820279792, 0.639043820279792, 
    0.639043820279792, 0.639043820279792, 0.639043820279792, 
    0.295199402942561, 0.295199402942561, 0.295199402942561, 
    0.295199402942561, 0.295199402942561, 0.295199402942561, 
    0.114491497757798, 0.114491497757798, 0.114491497757798, 
    0.114491497757798, 0.114491497757798, 0.114491497757798, 
    9.24810159594489e-05)), class = c("tbl_df", "tbl", "data.frame"
), row.names = c(NA, -37L), .Names = c("total.projects", "category", 
"total.workers")) %>% unique()

highchart() %>%
  hc_add_series(pyramid_data,
                "bar",
                hcaes(y = total.projects,
                      x = category),
                name = "Projects") %>%
  hc_add_series(pyramid_data,
                "bar",
                hcaes(y = -1 * total.workers,
                      x = category),
                name = "Workers") %>%
  hc_plotOptions(series = list(stacking = "normal"),
                 bar = list(minPointLength = 3)) %>%
  hc_xAxis(
    list(
      categories = pyramid_data$category,
      reversed = TRUE,
      opposite = FALSE
    ),
    list(
      opposite = TRUE,
      reversed = TRUE,
      categories = pyramid_data$category,
      linkedTo = 0
    )
  ) %>%
  hc_yAxis(labels = list(
    formatter = JS("function () {
                   return Math.abs(this.value) + '%';
                   }")
  )) %>%
  hc_tooltip(
    formatter = JS(
      "function () {
      return '<b>' + this.series.name + ' in ' + this.point.category + '</b><br/>' +
      Highcharts.numberFormat(Math.abs(this.point.y), 2);
      }"
)
    )
ox-it / oidnChaRts

Add a population_pyramid function #42
