input.lua
--- Iterators for extracting words or numbers from an input source.
--
-- require 'pl'
-- local total,n = seq.sum(input.numbers())
-- print('average',total/n)
--
-- _source_ is defined as a string or a file-like object (i.e. has a read() method which returns the next line)
--
-- See here
--
-- Dependencies: pl.utils
-- @module pl.input
local strfind = string.find
local strsub = string.sub
local strmatch = string.match
local utils = require 'pl.utils'
local unpack = utils.unpack
local pairs,type,tonumber = pairs,type,tonumber
local patterns = utils.patterns
local io = io
local assert_arg = utils.assert_arg
local input = {}
--- create an iterator over all tokens.
-- based on allwords from PiL, 7.1
-- @func getter any function that returns a line of text
-- @string pattern
-- @string[opt] fn Optionally can pass a function to process each token as it's found.
-- @return an iterator
function input.alltokens (getter,pattern,fn)
local line = getter() -- current line
local pos = 1 -- current position in the line
return function () -- iterator function
while line do -- repeat while there are lines
local s, e = strfind(line, pattern, pos)
if s then -- found a word?
pos = e + 1 -- next position is after this token
local res = strsub(line, s, e) -- return the token
if fn then res = fn(res) end
return res
else
line = getter() -- token not found; try next line
pos = 1 -- restart from first position
end
end
return nil -- no more lines: end of traversal
end
end
local alltokens = input.alltokens
-- question: shd this _split_ a string containing line feeds?
--- create a function which grabs the next value from a source. If the source is a string, then the getter
-- will return the string and thereafter return nil. If not specified then the source is assumed to be stdin.
-- @param f a string or a file-like object (i.e. has a read() method which returns the next line)
-- @return a getter function
function input.create_getter(f)
if f then
if type(f) == 'string' then
local ls = utils.split(f,'\n')
local i,n = 0,#ls
return function()
i = i + 1
if i > n then return nil end
return ls[i]
end
else
-- anything that supports the read() method!
if not f.read then error('not a file-like object') end
return function() return f:read() end
end
else
return io.read -- i.e. just read from stdin
end
end
--- generate a sequence of numbers from a source.
-- @param f A source
-- @return An iterator
function input.numbers(f)
return alltokens(input.create_getter(f),
'('..patterns.FLOAT..')',tonumber)
end
--- generate a sequence of words from a source.
-- @param f A source
-- @return An iterator
function input.words(f)
return alltokens(input.create_getter(f),"%w+")
end
local function apply_tonumber (no_fail,...)
local args = {...}
for i = 1,#args do
local n = tonumber(args[i])
if n == nil then
if not no_fail then return nil,args[i] end
else
args[i] = n
end
end
return args
end
--- parse an input source into fields.
-- By default, will fail if it cannot convert a field to a number.
-- @param ids a list of field indices, or a maximum field index
-- @string delim delimiter to parse fields (default space)
-- @param f a source @see create_getter
-- @tab opts option table, {no_fail=true}
-- @return an iterator with the field values
-- @usage for x,y in fields {2,3} do print(x,y) end -- 2nd and 3rd fields from stdin
function input.fields (ids,delim,f,opts)
local sep
local s
local getter = input.create_getter(f)
local no_fail = opts and opts.no_fail
local no_convert = opts and opts.no_convert
if not delim or delim == ' ' then
delim = '%s'
sep = '%s+'
s = '%s*'
else
sep = delim
s = ''
end
local max_id = 0
if type(ids) == 'table' then
for i,id in pairs(ids) do
if id > max_id then max_id = id end
end
else
max_id = ids
ids = {}
for i = 1,max_id do ids[#ids+1] = i end
end
local pat = '[^'..delim..']*'
local k = 1
for i = 1,max_id do
if ids[k] == i then
k = k + 1
s = s..'('..pat..')'
else
s = s..pat
end
if i < max_id then
s = s..sep
end
end
local linecount = 1
return function()
local line,results,err
repeat
line = getter()
linecount = linecount + 1
if not line then return nil end
if no_convert then
results = {strmatch(line,s)}
else
results,err = apply_tonumber(no_fail,strmatch(line,s))
if not results then
utils.quit("line "..(linecount-1)..": cannot convert '"..err.."' to number")
end
end
until #results > 0
return unpack(results)
end
end
return input