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--- Manipulating sequences as iterators.
-- @class module
-- @name pl.seq
local next,assert,type,pairs,tonumber,type,setmetatable,getmetatable,_G = next,assert,type,pairs,tonumber,type,setmetatable,getmetatable,_G
local strfind = string.find
local strmatch = string.match
local format = string.format
local mrandom = math.random
local remove,tsort,tappend = table.remove,table.sort,table.insert
local io = io
local utils = require 'pl.utils'
local function_arg = utils.function_arg
local _List = utils.stdmt.List
local _Map = utils.stdmt.Map
local assert_arg = utils.assert_arg
require 'debug'
--[[
module("pl.seq",utils._module)
]]
local seq = {}
-- given a number, return a function(y) which returns true if y > x
-- @param x a number
function seq.greater_than(x)
return function(v)
return tonumber(v) > x
end
end
-- given a number, returns a function(y) which returns true if y < x
-- @param x a number
function seq.less_than(x)
return function(v)
return tonumber(v) < x
end
end
-- given any value, return a function(y) which returns true if y == x
-- @param x a value
function seq.equal_to(x)
if type(x) == "number" then
return function(v)
return tonumber(v) == x
end
else
return function(v)
return v == x
end
end
end
--- given a string, return a function(y) which matches y against the string.
-- @param s a string
function seq.matching(s)
return function(v)
return strfind(v,s)
end
end
--- sequence adaptor for a table. Note that if any generic function is
-- passed a table, it will automatically use seq.list()
-- @param t a list-like table
-- @usage sum(list(t)) is the sum of all elements of t
-- @usage for x in list(t) do...end
function seq.list(t)
assert_arg(1,t,'table')
local key,value
return function()
key,value = next(t,key)
return value
end
end
--- return the keys of the table.
-- @param t a list-like table
-- @return iterator over keys
function seq.keys(t)
assert_arg(1,t,'table')
local key,value
return function()
key,value = next(t,key)
return key
end
end
local list = seq.list
local function default_iter(iter)
if type(iter) == 'table' then return list(iter)
else return iter end
end
iter = default_iter
--- create an iterator over a numerical range. Like the standard Python function xrange.
-- @param start a number
-- @param finish a number greater than start
function seq.range(start,finish)
local i = start - 1
return function()
i = i + 1
if i > finish then return nil
else return i end
end
end
-- count the number of elements in the sequence which satisfy the predicate
-- @param iter a sequence
-- @param condn a predicate function (must return either true or false)
-- @param optional argument to be passed to predicate as second argument.
function seq.count(iter,condn,arg)
local i = 0
seq.foreach(iter,function(val)
if condn(val,arg) then i = i + 1 end
end)
return i
end
--- return the minimum and the maximum value of the sequence.
-- @param iter a sequence
function seq.minmax(iter)
local vmin,vmax = 1e70,-1e70
for v in default_iter(iter) do
v = tonumber(v)
if v < vmin then vmin = v end
if v > vmax then vmax = v end
end
return vmin,vmax
end
--- return the sum and element count of the sequence.
-- @param iter a sequence
-- @param fn an optional function to apply to the values
function seq.sum(iter,fn)
local s = 0
local i = 0
for v in default_iter(iter) do
if fn then v = fn(v) end
s = s + v
i = i + 1
end
return s,i
end
--- create a table from the sequence. (This will make the result a List.)
-- @param iter a sequence
-- @return a List
-- @usage copy(list(ls)) is equal to ls
-- @usage copy(list {1,2,3}) == List{1,2,3}
function seq.copy(iter)
local res = {}
for v in default_iter(iter) do
tappend(res,v)
end
setmetatable(res,_List)
return res
end
--- create a table of pairs from the double-valued sequence.
-- @param iter a double-valued sequence
-- @return a list-like table
function seq.copy2 (iter,i1,i2)
local res = {}
for v1,v2 in iter,i1,i2 do
tappend(res,{v1,v2})
end
return res
end
--- create a table of 'tuples' from a multi-valued sequence.
-- A generalization of copy2 above
-- @param iter a multiple-valued sequence
-- @return a list-like table
function seq.copy_tuples (iter)
iter = default_iter(iter)
local res = {}
local row = {iter()}
while #row > 0 do
tappend(res,row)
row = {iter()}
end
return res
end
--- return an iterator of random numbers.
-- @param n the length of the sequence
-- @param l same as the first optional argument to math.random
-- @param u same as the second optional argument to math.random
-- @return a sequnce
function seq.random(n,l,u)
local rand
assert(type(n) == 'number')
if u then
rand = function() return mrandom(l,u) end
elseif l then
rand = function() return mrandom(l) end
else
rand = mrandom
end
return function()
if n == 0 then return nil
else
n = n - 1
return rand()
end
end
end
--- return an iterator to the sorted elements of a sequence.
-- @param iter a sequence
-- @param comp an optional comparison function (comp(x,y) is true if x < y)
function seq.sort(iter,comp)
local t = seq.copy(iter)
tsort(t,comp)
return list(t)
end
--- return an iterator which returns elements of two sequences.
-- @param iter1 a sequence
-- @param iter2 a sequence
-- @usage for x,y in seq.zip(ls1,ls2) do....end
function seq.zip(iter1,iter2)
iter1 = default_iter(iter1)
iter2 = default_iter(iter2)
return function()
return iter1(),iter2()
end
end
--- A table where the key/values are the values and value counts of the sequence.
-- This version works with 'hashable' values like strings and numbers. <br>
-- pl.tablex.count_map is more general.
-- @param iter a sequence
-- @return a map-like table
-- @return a table
-- @see pl.tablex.count_map
function seq.count_map(iter)
local t = {}
local v
for s in default_iter(iter) do
v = t[s]
if v then t[s] = v + 1
else t[s] = 1 end
end
return setmetatable(t,_Map)
end
-- given a sequence, return all the unique values in that sequence.
-- @param iter a sequence
-- @param returns_table true if we return a table, not a sequence
-- @return a sequence or a table; defaults to a sequence.
function seq.unique(iter,returns_table)
local t = count_map(iter)
local res = {}
for k in pairs(t) do tappend(res,k) end
table.sort(res)
if returns_table then
return res
else
return list(res)
end
end
-- print out a sequence @iter, with a separator @sep (default space)
-- and maximum number of values per line @nfields (default 7)
-- @fmt is an optional format function to create a representation of each value.
function seq.printall(iter,sep,nfields,fmt)
local write = io.write
if not sep then sep = ' ' end
if not nfields then
if sep == '\n' then nfields = 1e30
else nfields = 7 end
end
if fmt then
local fstr = fmt
fmt = function(v) return format(fstr,v) end
end
local k = 1
for v in default_iter(iter) do
if fmt then v = fmt(v) end
if k < nfields then
write(v,sep)
k = k + 1
else
write(v,'\n')
k = 1
end
end
write '\n'
end
-- return an iterator running over every element of two sequences (concatenation).
-- @param iter1 a sequence
-- @param iter2 a sequence
function seq.splice(iter1,iter2)
iter1 = default_iter(iter1)
iter2 = default_iter(iter2)
local iter = iter1
return function()
local ret = iter()
if ret == nil then
if iter == iter1 then
iter = iter2
return iter()
else return nil end
else
return ret
end
end
end
--- return a sequence where every element of a sequence has been transformed
-- by a function. If you don't supply an argument, then the function will
-- receive both values of a double-valued sequence, otherwise behaves rather like
-- tablex.map.
-- @param iter a sequence of one or two values
-- @param fn a function to apply to elements; may take two arguments
-- @param arg optional argument to pass to function.
function seq.map(fn,iter,arg)
fn = function_arg(1,fn)
iter = default_iter(iter)
return function()
local v1,v2 = iter()
if v1 == nil then return nil end
if arg then return fn(v1,arg) or false
else return fn(v1,v2) or false
end
end
end
--- filter a sequence using a predicate function
-- @param iter a sequence of one or two values
-- @param pred a boolean function; may take two arguments
-- @param arg optional argument to pass to function.
function seq.filter (iter,pred,arg)
pred = function_arg(2,pred)
return function ()
local v1,v2
while true do
v1,v2 = iter()
if v1 == nil then return nil end
if arg then
if pred(v1,arg) then return v1,v2 end
else
if pred(v1,v2) then return v1,v2 end
end
end
end
end
--- 'reduce' a sequence using a binary function.
-- @param fun a function of two arguments
-- @param iter a sequence
-- @param oldval optional initial value
-- @usage seq.reduce(operator.add,seq.list{1,2,3,4}) == 10
-- @usage seq.reduce('-',{1,2,3,4,5}) == -13
function seq.reduce (fun,iter,oldval)
fun = function_arg(1,fun)
iter = default_iter(iter)
if not oldval then
oldval = iter()
end
local val = oldval
for v in iter do
val = fun(val,v)
end
return val
end
--- take the first n values from the sequence.
-- @param iter a sequence of one or two values
-- @param n number of items to take
-- @return a sequence of at most n items
function seq.take (iter,n)
local i = 1
iter = default_iter(iter)
return function()
if i > n then return end
local val1,val2 = iter()
if not val1 then return end
i = i + 1
return val1,val2
end
end
--- skip the first n values of a sequence
-- @param iter a sequence of one or more values
-- @param n number of items to skip
function seq.skip (iter,n)
n = n or 1
for i = 1,n do iter() end
return iter
end
--- a sequence with a sequence count and the original value. <br>
-- enum(copy(ls)) is a roundabout way of saying ipairs(ls).
-- @param iter a single or double valued sequence
-- @return sequence of (i,v), i = 1..n and v is from iter.
function seq.enum (iter)
local i = 0
iter = default_iter(iter)
return function ()
local val1,val2 = iter()
if not val1 then return end
i = i + 1
return i,val1,val2
end
end
--- map using a named method over a sequence.
-- @param iter a sequence
-- @param name the method name
-- @param arg1 optional first extra argument
-- @param arg2 optional second extra argument
function seq.mapmethod (iter,name,arg1,arg2)
iter = default_iter(iter)
return function()
local val = iter()
if not val then return end
local fn = val[name]
if not fn then error(type(val).." does not have method "..name) end
return fn(val,arg1,arg2)
end
end
--- a sequence of (last,current) values from another sequence.
-- This will return S(i-1),S(i) if given S(i)
-- @param iter a sequence
function seq.last (iter)
iter = default_iter(iter)
local l = iter()
if l == nil then return nil end
return function ()
local val,ll
val = iter()
if val == nil then return nil end
ll = l
l = val
return val,ll
end
end
--- call the function on each element of the sequence.
-- @param iter a sequence with up to 3 values
-- @param fn a function
function seq.foreach(iter,fn)
fn = function_arg(2,fn)
for i1,i2,i3 in default_iter(iter) do fn(i1,i2,i3) end
end
---------------------- Sequence Adapters ---------------------
local SMT
local callable = utils.is_callable
local function SW (iter,...)
if callable(iter) then
return setmetatable({iter=iter},SMT)
else
return iter,...
end
end
-- can't directly look these up in seq because of the wrong argument order...
local map,reduce,mapmethod = seq.map, seq.reduce, seq.mapmethod
local overrides = {
map = function(self,fun,arg)
return map(fun,self,arg)
end,
reduce = function(self,fun)
return reduce(fun,self)
end
}
SMT = {
__index = function (tbl,key)
local s = overrides[key] or seq[key]
if s then
return function(sw,...) return SW(s(sw.iter,...)) end
else
return function(sw,...) return SW(mapmethod(sw.iter,key,...)) end
end
end,
__call = function (sw)
return sw.iter()
end,
}
setmetatable(seq,{
__call = function(tbl,iter)
if not callable(iter) then
if type(iter) == 'table' then iter = seq.list(iter)
else return iter
end
end
return setmetatable({iter=iter},SMT)
end
})
--- create a wrapped iterator over all lines in the file.
-- @param f either a filename or nil (for standard input)
-- @return a sequence wrapper
function seq.lines (f)
local iter = f and io.lines(f) or io.lines()
return SW(iter)
end
function seq.import ()
_G.debug.setmetatable(function() end,{
__index = function(tbl,key)
local s = overrides[key] or seq[key]
if s then return s
else
return function(s,...) return seq.mapmethod(s,key,...) end
end
end
})
end
return seq
|