Part 1 – Word Count
This problem asks you to write a function word_count that counts how many times words occur in a piece of text. This function must have the type
string -> (string * int) list
and be in a file named word_count.ml .
For this problem, you must follow a rather prescribed sequence of steps to implement this function. The reason for this is to provide an example of how data, in this case text, can be repeatedly transformed until the result is acquired. In the next problem you will have to decide what this sequence of transformations is for yourself.
The prescribed process takes the name of a file as input (as a string ) and returns a list of pairs indicating how many times a word (again as a string ) appears in the contents of the file.
The file demo.txt in the Homework/Files directory in the public class repository contains a short paragraph of text. The word “punctuation” appears 3 times and the word “about” appears 1 time. Thus the pairs (“punctuation”, 3) and (“about”, 1) should appear somewhere in the output of
word_count “../../public-class-repo/Homeworks/Files/demo.txt ”
Your program is to transform the original data (the filename) into the result in 7 steps. In fact, you should use the following implementation of word_count and provide implementations for the six transform functions.
let word_count (fn: string) : (string * int) list =
let step1: char list = read_file fn in
let step2: char list list = transform1 step1 in
let step3: string list = transform2 step2 in
let step4: string list = transform3 step3 in
let step5: (string * int) list = transform4 step4 in
let step6: (string * int list) list = transform5 step5 in
let step7: (string * int) list = transform6 step6 in
step7
From this code, it is clear that each of the six transform functions takes a single input, computed in the previous step, and returns a result consumed in the following step.
Your job is to implement the six transform functions.
** NEW ** A description of the 7 step values is below and ths should clarify questions you may have.
step1 is just the contents of the input file
step2 is the result of splitting the file contents into chuncks at any appropriate separator. If two separators (say a space and a comma) are next to each other, then an empty list would be in thils list to indicate that there were 0 characters between these two separators.
step3 should convert these char list words into strings
step4 should remove the empty words.
step5 constructs a pair (s,1) for each string s in step4
step6 groups these together so that all pairs with the same string are collected together so
all the 1 values are put into the same list.
step7 adds up the values in the lists in each pair to obtain the count
NEWER * Here is a sample interaction using the instructors solution. This uses a new sample file pets.txt that is now in the public-class-repo.
utop # let step1 = read_file “../../public-class-
repo/Homeworks/Files/pets.txt” ;;
val step1 : char list =
[‘d’; ‘o’; ‘g’; ‘
’; ‘c’; ‘a’; ‘t’; ‘
’; ‘c’; ‘a’; ‘t’; ‘
’; ‘d’; ‘o’;
‘g’; ‘
’; ‘
’; ‘
’; ‘c’; ‘h’; ‘i’; ‘c’; ‘k’; ‘e’; ‘n’; ‘
’; ‘c’; ‘h’;
‘i’; ‘c’; ‘k’; ‘e’; ‘n’; ‘
’; ‘c’; ‘o’; ‘w’; ‘
’; ‘d’; ‘o’; ‘g’; ‘
’]
ý¡è( 12:53:34 )ý¡è< command 25>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop # let step2 = transform1 step1 ;;
val step2 : char list list =
[[‘d’; ‘o’; ‘g’]; [‘c’; ‘a’; ‘t’]; [‘c’; ‘a’; ‘t’]; [‘d’; ‘o’; ‘g’];
[]; []; [‘c’; ‘h’; ‘i’; ‘c’; ‘k’; ‘e’; ‘n’];
[‘c’; ‘h’; ‘i’; ‘c’; ‘k’; ‘e’; ‘n’]; [‘c’; ‘o’; ‘w’]; [‘d’; ‘o’; ‘g’];
[]]
ý¡è( 12:53:49 )ý¡è< command 26>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop # let step3 = transform2 step2 ;;
val step3 : string list =
[“dog”; “cat”; “cat”; “dog”; “”; “”; “chicken”; “chicken”; “cow”; “dog”; “”]
ý¡è( 12:54:00 )ý¡è< command 27>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop # let step4 = transform3 step3 ;;
val step4 : string list =
[“dog”; “cat”; “cat”; “dog”; “chicken”; “chicken”; “cow”; “dog”]
ý¡è( 12:54:14 )ý¡è< command 28>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop # let step5 = transform4 step4 ;;
val step5 : (string * int) list =
[(“dog”, 1); (“cat”, 1); (“cat”, 1); (“dog”, 1); (“chicken”, 1);
(“chicken”, 1); (“cow”, 1); (“dog”, 1)]
ý¡è( 12:54:33 )ý¡è< command 29>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop # let step6 = transform5 step5 ;;
val step6 : (string * int list) list =
[(“dog”, [1; 1; 1]); (“cow”, [1]); (“chicken”, [1; 1]); (“cat”, [1; 1])]
ý¡è( 12:54:42 )ý¡è< command 30>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop # let step7 = transform6 step6 ;;
val step7 : (string * int) list =
[(“dog”, 3); (“cow”, 1); (“chicken”, 2); (“cat”, 2)]
ý¡è( 12:55:03 )ý¡è< command 31>ý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡èý¡è{
counter: 0 }ý¡è
utop #
To assist in your effort, you may want to use the following functions and you are free to copy them into your word_count.ml file:
let read_file (file_name: string) : char list =
let ic = open_in file_name
in
let rec read_chars ic =
(* `input_char` raises an exception when it attempts to read
past the end of the file.This is caught to terminate
the `read_chars` function. *)
try
let next_char = input_char ic
in next_char :: read_chars ic
with
_ -> []
in read_chars ic
let implode (cs: char list) : string =
String.concat “” (List.map(String.make 1) cs)
let explode (s: string) : char list =
let l = String.length s
in
let rec f i =
if i = l then [] else s.[i] :: f (i+1)
in f 0
You might also like to use the lookup_all function found in the find_and_lookup.ml file in the Sample Programs directory of the public repository. With this you can add the following simple
tests to the bottom of your file and check that they always evaluate to true :
let demo_count = word_count “../../public-class-repo/Homeworks/Files/demo.txt”
let test1 = lookup_all “new” demo_count = [2]
let test2 = lookup_all “the” demo_count = [5]
let test3 = lookup_all “to” demo_count = [2]
let test4 = lookup_all “punctuation” demo_count = [3]
Finally, you might use the following function temporarily in transform1 to split the file contents into words:
While this will work on the demo.txt file, it is not sufficient for the other sample file Liverpool.txt . The demo.txt file is rather special because it only contains words separated by
a single newline character. Thus, splitting a character list ( chs above) into a list of list of characters by only splitting on a single character (where c is passed the character
) is Ok for this file. But for the Liverpool.txt file you need to recognize that other characters, such as a space, a comma, a period, or a sequence of these, also indicates a break between words.
Thus, you will eventually want to write a function split with the type ‘a list -> ‘a list -> ‘a list list
where the first argument is a list of “separators” (such as
[ ‘ ‘; ‘,’; ‘;’; ‘.’; ‘!’; ‘
’ ]
and maybe other characters that indicate the separation of words. The second argument is the input to be separated. In our case, this will be the character list in step1 .
The function transform5 may be the most interesting one. Here, you might consider using one of your partition functions from Homework 01. Some other interesting functions might also need to be written for this step.
No rec
Your solution must be one that uses higher order functions such as List.filter , List.map , List.fold_left , List.fold_right and others. The only recursive function (using the rec
keyword) allowed is the read_chars function inside the provided function read_file . Part 2 – Word Games
This problem asks you to write a function word_games that generates questions for a rapid-fire word game. This is inspired by this episode of the “Sunday Puzzle” show on NPR:
https://www.npr.org/2019/01/06/682575357/sunday-puzzle-stuck-in-the-middle
let incomplete_split (c: char) (chs: char list) : char list list =
List.map explode (String.split_on_char c (implode chs))
You will write two functions for this part:
answers : string -> string list
pretty_answers : string list -> (string * string) list
The primary work will be done by answers . It takes as input the name of a file containing a list of words are returns all 8 letter words that if the middle 2 letters are removed results in a 6 letter word also in the original list of words.
For example, if the file contains “accident” and “accent”, then answers will return the string “accident” in its output.
Getting started.
Create a file named word_games.ml that will contain your two functions. To it, add the following function for reading files:
let read_file (file_name: string) : char list =
let ic = open_in file_name
in
let rec read_chars ic =
try
let next_char = input_char ic
in next_char :: read_chars ic
with
_ -> []
in read_chars ic
This is the only function in this part that may contain the rec keyword. This function will return a list of characters. Since our output requires a list of strings, then you may want to add the following function to your file as well:
Also, your split function from Part 1 above will be useful. Copy that function into word_games.ml as well.
Finally, add the following two lines
These are file name paths to two sample dictionaries from inside your Hwk_02 directory. This arrangement assumes that your individual repository and the public class repository are both cloned into the same directory, as instructed in Lab 01.
This will allow you to test your work with the simple expressions answers d1 or answers d2 .
let implode (cs: char list) : string =
String.concat “” (List.map(String.make 1) cs)
let d1 = “../../public-class-repo/Homeworks/Files/words-small.txt”
let d2 = “../../public-class-repo/Homeworks/Files/words-google-10000.txt”
The answers function
The answers function will need to read in the contents of the given file. You may then want to
use split to group that original char list into a list of words, that is a char list list .
From here, consider extracting the words of length 8 and 6.
It should then be a matter extracting the appropriate words from the list of 8 letter words. Clarification: Say you have an 8 letter word named w8 , you want to check if the first three letters concatenated to the last 3 letters is a word from the list of 6 letter words. You might investigate how the library function String.sub works to extract these 3 letter words from an 8 letter word.
There are several ways one can go about solving this problem. It is probably wise to consider these steps in some details before you start programming.
That is, ask yourself how the input is transformed and what the OCaml type of those intermediate values will be.
The pretty_answers function.
This function is rather simple. It just takes the result from answers and converts it into a list of string pairs. The first is the 6 letter word, the second is the 8 letter word that contains the 6 letter word in its first and last 3 letter bits.
For example, here is the result of using both function in utop:
utop # pretty_answers (answers d2) ;;
– : (string * string) list =
[(“mating”, “matching”); (“offers”, “officers”); (“gaming”, “gambling”);
(“estate”, “estimate”); (“accent”, “accident”); (“caring”, “carrying”);
(“equity”, “equality”); (“states”, “statutes”); (“string”, “striking”);
(“though”, “thorough”)]
Note the file words-google-10000.txt comes from this repository:
https://github.com/first20hours/google-10000-english
Again, no rec
You solution must be one that uses higher order functions such as List.filter , List.map , List.fold_left , List.fold_right and others. The only recursive function (using the rec
keyword) allowed is the read_chars function inside the provided function read_file .
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