feat: add mathematical sorting for pure numeric lists

Pure number lists (only numeric values, including negatives, decimals, and
scientific notation) now sort mathematically when natural sort is enabled.
Mixed content continues using natural sort. Empty segments are treated as 0.

Author: sQVe

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Mathematical sorting for pure numeric lists. When natural sort is enabled and all items are numbers (integers, decimals, scientific notation), sorting uses numeric comparison. `-90, -10, 5` now sorts correctly instead of lexicographically.
+
 ### Fixed
 
 - Natural sorting now treats dashes as separators, not negative signs. `item-10, item-2` sorts as `item-2, item-10` instead of reversed (#18).

lua/sort/sort.lua

@@ -8,8 +8,13 @@ local M = {}
 --- @param a string
 --- @param b string
 --- @param options SortOptions
+--- @param use_math_sort? boolean
 --- @return boolean
-local function compare_strings(a, b, options)
+local function compare_strings(a, b, options, use_math_sort)
+  if use_math_sort then
+    return utils.math_compare(a, b)
+  end
+
   -- Use natural sorting if enabled.
   if options.natural then
     return utils.natural_compare(a, b, options.ignore_case)
@@ -129,12 +134,14 @@ M.delimiter_sort = function(text, options)
     original_order[i] = item.original_position
   end
 
+  local use_math_sort = options.natural and utils.all_pure_numbers(items)
+
   -- Sort items by their trimmed content.
   table.sort(items, function(a, b)
     if options.reverse then
-      return compare_strings(b.trimmed, a.trimmed, options)
+      return compare_strings(b.trimmed, a.trimmed, options, use_math_sort)
     else
-      return compare_strings(a.trimmed, b.trimmed, options)
+      return compare_strings(a.trimmed, b.trimmed, options, use_math_sort)
     end
   end)
 
@@ -302,12 +309,15 @@ M.line_sort_text = function(text, options)
     items_to_sort = line_items
   end
 
+  local use_math_sort = options.natural
+    and utils.all_pure_numbers(items_to_sort)
+
   -- Sort lines using the same comparison logic as delimiter sorting but on trimmed content.
   table.sort(items_to_sort, function(a, b)
     if options.reverse then
-      return compare_strings(b.trimmed, a.trimmed, options)
+      return compare_strings(b.trimmed, a.trimmed, options, use_math_sort)
     else
-      return compare_strings(a.trimmed, b.trimmed, options)
+      return compare_strings(a.trimmed, b.trimmed, options, use_math_sort)
     end
   end)
 

lua/sort/utils.lua

@@ -354,4 +354,45 @@ M.normalize_whitespace = function(
   return dominant_pattern
 end
 
+--- Rejects '.5', accepts '0.5' and '5.'.
+--- @param str string
+--- @return boolean
+M.is_pure_number = function(str)
+  if str == nil or str == '' then
+    return false
+  end
+  local has_basic_number = string.match(str, '^[%+%-]?%d+%.?%d*$') ~= nil
+  local has_scientific = string.match(str, '^[%+%-]?%d+%.?%d*[eE][%+%-]?%d+$')
+    ~= nil
+  return (has_basic_number or has_scientific) and tonumber(str) ~= nil
+end
+
+--- Check if all non-empty items in a list are pure numbers.
+--- Returns true for empty arrays or arrays with only empty trimmed values.
+--- This triggers mathematical sorting for pure number lists and empty segments.
+--- @param items table[] Array of items with trimmed field
+--- @return boolean
+M.all_pure_numbers = function(items)
+  for _, item in ipairs(items) do
+    if item.trimmed ~= '' and not M.is_pure_number(item.trimmed) then
+      return false
+    end
+  end
+  return true
+end
+
+--- Falls back to string comparison if tonumber fails (should not occur when
+--- called via the sorting pipeline which pre-validates with all_pure_numbers).
+--- @param a string
+--- @param b string
+--- @return boolean
+M.math_compare = function(a, b)
+  local na = a == '' and 0 or tonumber(a)
+  local nb = b == '' and 0 or tonumber(b)
+  if na and nb then
+    return na < nb
+  end
+  return a < b
+end
+
 return M