Merge pull request #2471 from saulpw/kef/typesheet

[docs] expand TypeSheet.md

visidata/guides/TypesSheet.md

@@ -1,6 +1,6 @@
 # Types
 
-Columns usually begin as untyped (`anytype`), but can be set.
+Columns usually begin as untyped (`anytype`), but can be set to specific types.
 
 - {help.commands.type-any}
 - {help.commands.type-currency}
@@ -10,4 +10,34 @@ Columns usually begin as untyped (`anytype`), but can be set.
 - {help.commands.type-len}
 - {help.commands.type-string}
 
-*Note*: `float` uses the decimal separator; `currency` removes non-numeric characters and parses as float; `date` parses dates into ISO8601 format; `len` formats the cell value to the length of the content.
+## Type formatting
+
+VisiData pre-set defaults for formatting types:
+
+- `currency` removes non-numeric characters and parses the remainder as `float`.
+- `date` parses dates into date object (shown as ISO8601).
+- `vlen` formats the cell value to the length of the content
+- `float` uses the decimal seperator, keeping two significant digits.
+
+Change float precision with:
+- {help.commands.setcol-precision-less}
+- {help.commands.setcol-precision-more}
+
+To change the default fmtstr for a type:
+
+- {help.options.disp_currency_fmt}
+- {help.options.color_currency_neg}
+- {help.options.disp_date_fmt}
+- {help.options.disp_float_fmt}
+- {help.options.disp_int_fmt}
+
+
+## Importance of typing
+
+Certain commands behave differently depending on how the column is typed.
+
+Grouping by a numeric column in a Frequency table can result in numeric range binning. Grouping by a string results in categorical binning.
+
+Un-typed columns (`anytype`) often default to `string`-like behaviour. Errors when working with numerical or datetime data is often due to values being considered as strings.
+
+For example. [:code]addcol-expr col1+col2[/] results in a concatenation of the two columns when they are `anytype`, and addition when they are numerical.