table_source: Create an experimental lazy table source

In termr: Modern Reactive Terminal Applications with Data Workflows

Create an experimental lazy table source

Description

A table source lets data_table() request only the rows it needs. All callbacks are synchronous. get_rows() must return a data frame with the requested columns in the requested order. Row counts are known.

Usage

table_source(
  row_count,
  column_names,
  get_rows,
  sort = NULL,
  filter = NULL,
  search = NULL,
  row_key = NULL,
  set_value = NULL,
  refresh = NULL,
  close = NULL,
  on_error = NULL
)

Arguments

row_count	Function returning the current number of rows, or a non-negative scalar count.
column_names	Function returning unique, non-empty names, or a character vector.
get_rows	Function ⁠function(start, count, columns = NULL)⁠.
sort, filter, search	Optional delegated operations.
row_key	Optional function mapping view positions to row keys.
set_value	Optional function ⁠(row, column, value)⁠ for editing.
refresh, close	Optional functions called by ⁠$refresh()⁠ and ⁠$close()⁠.
on_error	Optional function returning a page-shaped placeholder when get_rows() fails. It receives the original condition and requested page.

Details

Optional sort and filter callbacks change the source's current view. They receive the sort keys or the named filter list used by DataTable$sort() and DataTable$filter_columns(). Returning FALSE rejects the operation; returning NULL or TRUE accepts it. A source should expose only operations it can implement without materializing its entire data set.

search receives a parsed query, column names, start, direction, and include_current; it returns NULL or list(position, column). row_key maps view positions to stable row identities. set_value(row, column, value) receives a current view position. refresh and close are optional lifecycle callbacks. on_error(error, start, count, columns) may return a correctly shaped placeholder data frame when a page read fails; the table then displays the error instead of aborting a paint. Closing a source is explicit and never closes resources the source does not own.

Value

An experimental termr_table_source object.

termr documentation built on Oct. 21, 2026, 5:13 p.m.