[guides] Add a FrequencyTable Guide (#2534)

Co-authored-by: anjakefala <[email protected]>

visidata/aggregators.py

@@ -288,7 +288,7 @@ def _fmt_aggr_summary(match, row, trigger_key):
             vd.warning(f'aggregator does not exist: {aggr}')
     return aggrs
 
-Sheet.addCommand('+', 'aggregate-col', 'addAggregators([cursorCol], chooseAggregators())', 'Add aggregator to current column')
+Sheet.addCommand('+', 'aggregate-col', 'addAggregators([cursorCol], chooseAggregators())', 'add aggregator to current column')
 Sheet.addCommand('z+', 'memo-aggregate', 'cursorCol.memo_aggregate(chooseAggregators(), selectedRows or rows)', 'memo result of aggregator over values in selected rows for current column')
 ColumnsSheet.addCommand('g+', 'aggregate-cols', 'addAggregators(selectedRows or source[0].nonKeyVisibleCols, chooseAggregators())', 'add aggregators to selected source columns')
 

visidata/guides/FrequencyTable.md

@@ -0,0 +1,42 @@
+# Frequency Tables are how you GROUP BY
+
+Frequency Tables group rows into bins by column value, and includes summary columns for source columns with aggregators.
+
+Set `--numeric-binning` to bin numeric rows into ranges instead of discrete values.
+
+- {help.commands.freq_col}
+
+- {help.commands.freq_keys}
+
+- {help.commands.freq_summary} 
+
+## Aggregators
+
+A **Frequency Table** contains a summary columns for each aggregator added to a source column.
+These aggregators need to be added before creating the Frequency Table.
+Examples of aggregators include min, max, sum, distinct, count, and list.
+
+- {help.commands.aggregate-col}
+
+Note: set an appropriate type for the aggregator target column, for example {help.commands.type_float}.
+
+## Explore the data
+
+Dive into a group to see the underlying row(s) using the **Frequency Table**:
+
+- {help.commands.open_row}
+- {help.commands.dive_selected}
+
+Select a group to select all of its underlying rows in the source sheet.
+
+## Using Split Panes with Frequency Tables
+
+Press `Shift+Z` to open a split pane, and then `Shift+F` to create a **Frequency Table**. The **Frequency Table** will automatically open in the other pane.
+
+See the `SplitpanesGuide` for more.
+
+#### Options
+
+- {help.options.disp_histogram}
+- {help.options.histogram_bins}
+- {help.options.numeric_binning}