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+--- 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 @{06-data.md.Reading_Unstructured_Text_Data|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 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
+