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[modified] refactored insert_sorted to get PR #18 merged
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tablex.lua
84
tablex.lua
@ -48,68 +48,50 @@ function tablex.unshift(t, v)
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return t
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end
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function tablex.is_sorted(t)
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local sorted = true
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for i = 1, #t - 1 do
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if t[i] > t[i + 1] then
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sorted = false
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break
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end
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end
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return sorted
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--default comparison; hoisted for clarity
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--(shared with sort.lua and suggests the sorted functions below should maybe be refactored there)
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local function default_less(a, b)
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return a < b
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end
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--check if a function is sorted based on a "less" or "comes before" ordering comparison
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--if any item is "less" than the item before it, we are not sorted
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--(use stable_sort to )
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function tablex.is_sorted(t, less)
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less = less or default_less
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for i = 1, #t - 1 do
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if less(t[i + 1], t[i]) then
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return false
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end
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end
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return true
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end
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--insert to the first position before the first larger element in the table
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--if this is used on an already sorted table, the table will remain sorted and not need re-sorting
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--todo: make it do binary search rather than linear to improve performance
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--(you can check if the table is sorted and sort if needed if you don't know)
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--return the table for possible chaining
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function tablex.insert_sorted(t, v, less)
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local inserted = false
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-- to use binary search is necessary as precondition that
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-- the table is sorted
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if not tablex.is_sorted(t) then
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for i = 1, #t do
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if less(v, t[i]) then
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table.insert(t, i, v)
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inserted = true
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break
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end
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end
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if not inserted then
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table.insert(t, v)
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end
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return t
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end
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local l = 1
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local r = #t
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if r < l then
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table.insert(t,v)
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return t
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end
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while l <= r do
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local mid = math.floor(l + (r - l) / 2)
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if (less(v, t[mid]) or v == t[mid]) and (mid == 1 or less(t[mid - 1], v) or t[mid - 1] == v) then
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table.insert(t, mid, v)
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inserted = true
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less = less or default_less
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local low = 1
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local high = #t
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local match
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while low <= high do
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local mid = math.floor((low + high) / 2)
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local mid_val = t[mid]
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if less(v, mid_val) then
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high = mid - 1
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elseif less(mid_val, v) then
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low = mid + 1
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else
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match = mid
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break
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elseif less(t[mid], v) then
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l = mid + 1
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elseif less(v, t[mid - 1]) then
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r = mid - 1
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end
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end
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if not inserted then
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table.insert(t, l, v)
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end
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table.insert(t, match or low, v)
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return t
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end
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--find the index in a sequential table that a resides at
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--or nil if nothing was found
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function tablex.index_of(t, a)
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