How to Match A Substring Ignoring the Case In Erlang?

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In Erlang, there are several ways to match a substring while ignoring the case. Here are three common approaches:

  1. Using the re module: The re module in Erlang provides functions for regular expression matching. You can use the re:run/3 function to match a substring while ignoring the case. Here's an example: String = "Hello World", Substring = "hello", Options = [caseless], % Ignore case {match, _} = re:run(String, Substring, Options), io:format("Substring matched!~n"). In this example, the re:run/3 function matches the Substring in the String while ignoring the case by specifying the caseless option. If a match is found, the function returns {match, _}. You can then handle this match accordingly.
  2. Using binary pattern matching: Erlang supports pattern matching on binaries. You can convert both the string and substring to lowercase or uppercase and then match them using pattern matching. Here's an example: String = "Hello World", Substring = "hello", LowerString = string:to_lower(String), LowerSubstring = string:to_lower(Substring), case LowerString of _LowerSubstring -> io:format("Substring matched!~n"); _ -> io:format("Substring not matched!~n") end. In this example, the string:to_lower/1 function is used to convert both the String and Substring to lowercase. The pattern matching then compares the transformed strings. If they match, the substring is considered to be found.
  3. Using the string module: The string module in Erlang also provides functions for working with strings. You can use the string:strcasestr/2 function to match a substring while ignoring the case. Here's an example: String = "Hello World", Substring = "hello", case string:strcasestr(String, Substring) of Found -> io:format("Substring matched at position ~w!~n", [Found]); _ -> io:format("Substring not matched!~n") end. In this example, the string:strcasestr/2 function searches for the Substring in the String while ignoring the case. If a match is found, it returns the position at which the substring starts. You can then handle this position accordingly.

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What is the behavior of the 'string' module functions when performing case-insensitive substring matching in Erlang?

The 'string' module functions in Erlang do not specifically provide built-in support for case-insensitive substring matching. The functions provided by the 'string' module (such as 'str:substr/3' or 'str:contains/2') perform case-sensitive substring matching.


To achieve case-insensitive substring matching, you would need to convert the strings to a common case (e.g., uppercase or lowercase) before performing the matching. You can use the 'string:to_upper/1' or 'string:to_lower/1' functions from the 'string' module to convert the strings to a specific case.


For example, if you want to perform case-insensitive substring matching using 'str:substr/3', you can convert both the source string and the substring to lowercase before performing the matching:

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Source = "Hello World",
Substring = "WORLD",
Match = str:substr(string:to_lower(Source), string:to_lower(Substring), 1).


In this example, the lowercase versions of the 'Source' and 'Substring' strings are used for matching, satisfying the case-insensitive condition.


It's important to note that this approach does not provide a direct case-insensitive matching capability with the 'string' module functions.


How to modify the standard substring matching function in Erlang to be case-insensitive?

To modify the standard substring matching function in Erlang to be case-insensitive, you can follow these steps:

  1. Open a new file in your preferred text editor and save it with the .erl extension, for example, substring.erl.
  2. Define a new function substring_case_insensitive that takes two arguments: the main string and the substring to search for.
  3. Use the re:run/3 function from the Erlang re module to match the substring case-insensitively using regular expressions.
  4. Return true if there is a match or false if there is no match.
  5. Optionally, you can add an additional clause to handle empty strings or handle edge cases as per your requirements.


Here's an example implementation of the modified case-insensitive substring matching function in Erlang:

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-module(substring).
-export([substring_case_insensitive/2]).

substring_case_insensitive(MainString, SubString) ->
    case re:run(MainString, SubString, [{case,less}]) of
        {match, _} -> true;
        nomatch -> false
    end.


Now, you can compile the module and test the function:

  1. Open a terminal and start the Erlang shell by executing the command erl.
  2. Compile the substring module by executing c(substring). in the Erlang shell.
  3. Call the substring_case_insensitive/2 function with a main string and a substring to test the case-insensitive substring matching, for example: substring:substring_case_insensitive("Hello World", "WORLD").


The function will return true since the substring is present case-insensitively in the main string.


What is the impact of string length on the efficiency of case-insensitive substring matching in Erlang?

In Erlang, the impact of string length on the efficiency of case-insensitive substring matching depends on the chosen algorithm and implementation.

  1. Naive Naïve algorithms would have a linear impact on efficiency with string length. The algorithm would compare each character of the substring with each character of the larger string, taking into account case insensitivity.
  2. Knuth-Morris-Pratt (KMP) Algorithm: The KMP algorithm aims to reduce unnecessary comparisons by utilizing a prefix table (also known as the failure function) that stores the length of the longest proper prefix of the pattern (substring) that is also a proper suffix. The KMP algorithm has a linear time complexity, which means the efficiency would still be impacted linearly by the length of the strings.
  3. Boyer-Moore Algorithm: The Boyer-Moore algorithm compares characters from right to left, and utilizes a bad character rule and a good suffix rule to skip unnecessary comparisons. The efficiency of the Boyer-Moore algorithm is generally faster than the KMP algorithm in practice, but the impact of string length can still be significant due to the initial pre-processing steps involved.


In conclusion, although more efficient algorithms like KMP or Boyer-Moore can improve the overall efficiency of case-insensitive substring matching, the impact of string length on efficiency remains linear for most practical scenarios.

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