How to render column total (with javascript) when using grouped rows in reactable r package?

Question

I am using crosstalk in combination with reactable. In the table I use grouped rows. Now I need to add a column total, using javascript.

---
title: "Focal Chart (Top)"
output: 
  flexdashboard::flex_dashboard:
    orientation: rows
---

Inputs {.sidebar}
-------------------------------------

```{r}
library(crosstalk)
library(reactable)
cars <- MASS::Cars93[1:20, c("Manufacturer", "Model", "Type", "Price")]

data <- SharedData$new(cars)
filter_checkbox("type", "Type", data, ~Type)
    filter_slider("price", "Price", data, ~Price, width = "100%")
    filter_select("mfr", "Manufacturer", data, ~Manufacturer)
```

Row {data-height=500}
-------------------------------------

### Chart 1

```{r}
reactable(
  data,
  groupBy = "Manufacturer",
  searchable = TRUE,
columns = list(
  Price = colDef(aggregated = JS("
      function(cellInfo) {
        // Calculate sum of all values in visible rows
        var values = cellInfo.subRows.map(function(row) { return row.Price})
        var total = values.reduce(function(a, b) { return a + b }, 0)
        return total.toFixed(1)
      }
    "),  footer = JS("function(colInfo) {
        var values = colInfo.data.map(function(row) { return row[colInfo.column.id] })
        var total = values.reduce(function(a, b) { return a + b }, 0)
        return '$' + total.toFixed(2)
      }")
    ),
    Manufacturer = colDef(footer = "Total")
  ),
  defaultColDef = colDef(footerStyle = list(fontWeight = "bold"))
)
```

Row {data-height=500}
-------------------------------------

### empty

```{r}

```   

### empty

```{r}

```

As you can see, the column total is $NaN. Ofcourse this is an unwanted outcome. If I remove the groupBy parameter, the column total is $471.80, as it should be. Does anyone know how to fix this groupBy behaviour? Many thanks in advance!

Answer 1

Originally answered at https://github.com/glin/reactable/issues/50, just copying it here:

This was an oversight in the reactable documentation -- the custom rendering docs don't mention what colInfo.data looks like when you have grouped/nested data: https://glin.github.io/reactable/articles/custom-rendering.html#footers

Usually, data will be an array of individual row data objects, like

{
  "Manufacturer": "Acura",
  "Model": "Integra",
  "Type": "Small",
  "Price": 15.9
}

However, when a row is aggregated, the individual sub row data will be nested under a _subRows property:

// For an aggregated row with 2 sub rows
{
  "Manufacturer": "Acura",
  "_subRows": [
    {
      "Manufacturer": "Acura",
      "Model": "Integra",
      "Type": "Small",
      "Price": 15.9
    },
    {
      "Manufacturer": "Acura",
      "Model": "Legend",
      "Type": "Midsize",
      "Price": 33.9
    }
  ]
}

You can insert a console.log(colInfo) in the JS function to explore the full data structure in your browser's JavaScript console:

footer = JS("function(colInfo) {
  console.log(colInfo)
}")

Since the individual row data is now nested, it's a little more work to sum it all up, but here's one method that uses two forEach loops:

library(reactable)

data <- MASS::Cars93[1:20, c("Manufacturer", "Model", "Type", "Price")]

reactable(
  data,
  groupBy = "Manufacturer",
  searchable = TRUE,
  columns = list(
    Price = colDef(
      aggregated = JS("function(cellInfo) {
        // Calculate sum of all values in visible rows
        var values = cellInfo.subRows.map(function(row) { return row.Price})
        var total = values.reduce(function(a, b) { return a + b }, 0)
        return total.toFixed(1)
      }"),
      footer = JS("function(colInfo) {
        var total = 0
        colInfo.data.forEach(function(row) { 
          row._subRows.forEach(function(data) { 
            total += data[colInfo.column.id]
          })
        })
        return '$' + total.toFixed(2)
      }")
    ),
    Manufacturer = colDef(footer = "Total")
  ),
  defaultColDef = colDef(footerStyle = list(fontWeight = "bold"))
)