[FIXED] How to convert a Roman numeral to integer in PHP?

Issue

Using PHP, I'd like to convert a string containing a Roman number into its integer representation. I need this because I need to make calculations on them.

Wikipedia on Roman numerals

It would suffice to only recognize the basic Roman numeral characters, like:

$roman_values=array(
    'I' => 1,
    'V' => 5,
    'X' => 10,
    'L' => 50,
    'C' => 100,
    'D' => 500,
    'M' => 1000,
);

That means the highest possible number is 3999 (MMMCMXCIX). I will use N to represent zero, other than that only positive integers are supported.

I cannot use the PEAR library for Roman numbers.

I found this great question on SO on how to test whether the string contains a valid Roman numeral:

How do you match only valid roman numerals with a regular expression?

What would be the best way of coding this?

Solution

How about this:

$romans = array(
    'M' => 1000,
    'CM' => 900,
    'D' => 500,
    'CD' => 400,
    'C' => 100,
    'XC' => 90,
    'L' => 50,
    'XL' => 40,
    'X' => 10,
    'IX' => 9,
    'V' => 5,
    'IV' => 4,
    'I' => 1,
);

$roman = 'MMMCMXCIX';
$result = 0;

foreach ($romans as $key => $value) {
    while (strpos($roman, $key) === 0) {
        $result += $value;
        $roman = substr($roman, strlen($key));
    }
}
echo $result;

which should output 3999 for the supplied $roman. It seems to work for my limited testing:

MCMXC = 1990
MM = 2000
MMXI = 2011
MCMLXXV = 1975

You might want to do some validation first as well :-)

Answered By - andyb

Answer Checked By - Mildred Charles (PHPFixing Admin)

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[FIXED] What does the f'+{value}' do? I was solving Roman to integer problem and I came across it

Issue

This is the code. The second line doesn't make much sense to me. Can anyone please help?

    for key, value in roman_map.items():
        s = s.replace(key, f'+{value}')
    return eval(s)

Solution

It's just for formatting the string, for example if the variable value is 3, then f'+{value}' would result as a formatted string '+3'. If this doesn't satisfy you, then I think I know what's confusing you, the line s = s.replace(key, f'+{value}') is a simple line which is for replacing a part of a string. As I see it, s is a pre defined variable with a string(it's written s = s.replace in the line, the replace method belongs to a string so most likely s is a string variable) so what this line does is, in the for loop, you see the key variable, now the replace method takes two parameters, the first one asks the user which part of the string to replace and the second specifies what to replace it with, henceforth I can say this much that this line replaces the part of the string which is same as whatever value the variable key holds during the current iteration(in simple english, the current loop number) with f'+{value}'.(Read my answer from the starting in case you forgot what that line means or if your confused, if this still doesen't satisfy you, try googling the string replace method and f strings in python)

Answered By - Devyansh

Answer Checked By - Robin (PHPFixing Admin)

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[FIXED] phpMyAdmin - mariaDB roman numerals function

Issue

can anybody help me with my sorting function - seriously I don't know how can I make it work as supposed to. :( Database is in MariaDB in Xampp. I use phpMyAdmin to execute the query.

DELIMITER $$

DROP FUNCTION IF EXISTS convRomanNumeral$$

CREATE FUNCTION convRomanNumeral (numeral CHAR(4))
  RETURNS INT
BEGIN
  DECLARE intnum INT;
    CASE numeral
      WHEN "I" THEN intnum = 1;
      WHEN "II" THEN intnum = 2;
    END CASE;
  RETURN intnum;
END;

$$

SET @iteration = -1;

UPDATE `st0gk_docman_documents` 
    SET created_on = DATE('2016-06-14') + INTERVAL(@iteration := @iteration + 1) SECOND
    WHERE `docman_category_id` = 141 ORDER BY convRomanNumeral(SUBSTRING(SUBSTRING_INDEX(title,'/',1),' ',-2) ASC, SUBSTRING_INDEX(title,'/',-2)+0 ASC;

So what I want to achieve is to sort documents by title. Example titles are:

• Document Nr I/36/2006
• Document Nr II/36/2006
• Document Nr I/32/2006
• Document Nr II/19/2006

After sorting them by first Roman number and then by second Arabic number I want to update the date. Code below for updating by only second Arabic number works properly:

SET @iteration = -1;

UPDATE `st0gk_docman_documents` 
    SET created_on = DATE('2016-06-14') + INTERVAL(@iteration := @iteration + 1) SECOND
    WHERE `docman_category_id` = 141 ORDER BY SUBSTRING_INDEX(title,'/',-2)+0 ASC;

I would like to use CASE to return proper variable for Roman values. I know it's not perfect but I can't even make the CASE and FUNCTION work. What I am doing wrong? All suggestions are welcome.

Solution

First mistake that I was making it was trying to execute the whole query at once... After taking the first lodge out of the way the debugging seemed way simpler. :D

So I created my case function to convert Roman numerals:

DELIMITER $$

DROP FUNCTION IF EXISTS convRomanNumeralSubFunction$$
CREATE FUNCTION convRomanNumeralSubFunction (numeral CHAR(1))
  RETURNS INT
BEGIN
  DECLARE intnum INT;
    CASE numeral
      WHEN "I" THEN SELECT 1 INTO intnum;
      WHEN "X" THEN SELECT 10 INTO intnum;
      WHEN "C" THEN SELECT 100 INTO intnum;
      WHEN "M" THEN SELECT 1000 INTO intnum;
      WHEN "V" THEN SELECT 5 INTO intnum;
      WHEN "L" THEN SELECT 50 INTO intnum;
      WHEN "D" THEN SELECT 500 INTO intnum;
    END CASE;
  RETURN intnum;
END;

$$

After that I declared the second function needed for conversion. I don't know if You can declare function inside function... and I didn't want to waste more time on this. For sure You can declare Function inside Procedure. Anyhow. WARNING: This function is not proof of BAD numerals like IIX. Numerals like that or will be badly counted. Also AXI will not count.

DELIMITER $$

DROP FUNCTION IF EXISTS convRomanNumeral$$
CREATE FUNCTION convRomanNumeral (numeral CHAR(10))
  RETURNS INT
BEGIN
  DECLARE currentintnum, previntnum, intnum, counter, numerallength INT;
  SET numerallength = LENGTH(numeral);
  SET counter = numerallength;
  SET intnum = 0;
  SET previntnum = 0;
  WHILE counter > 0 DO
      SET currentintnum = CAST(convRomanNumeralSubFunction(SUBSTRING(numeral,counter, 1)) as integer);
      IF currentintnum < previntnum THEN
        SET intnum = intnum - currentintnum;
      ELSE 
        SET intnum = intnum + currentintnum;
      END IF;
      SET previntnum = currentintnum;
      SET counter = counter - 1;
  END WHILE;
  RETURN intnum;
END;

$$

So that's it. Now You can convert all kind of Roman numerals and sort them up. Use this to test the conversion:

SELECT convRomanNumeral("XIX");

This is example sorting code that I in the end used:

SET @iteration = -1;

UPDATE `st0gk_docman_documents` 
    SET created_on = DATE('2016-06-07') + INTERVAL(@iteration := @iteration + 1) SECOND
    WHERE `docman_category_id` = 67 ORDER BY convRomanNumeralBreak(SUBSTRING_INDEX(SUBSTRING_INDEX(title,'/',1),' ',-1)) ASC, SUBSTRING_INDEX(title,'/',-2)+0 ASC;

Also one more thing - if You'll try to excecute this on mySQL then You have to fix this line:

SET currentintnum = CAST(convRomanNumeralSubFunction(SUBSTRING(numeral,counter, 1)) as integer);

into this:

SET currentintnum = CAST(convRomanNumeralSubFunction(SUBSTRING(numeral,counter, 1)) as SIGNED);

This code could be improved but as the @Rick James stated this should be done differently - not in as db update but in different table structure and sorting mechanism.

Answered By - Thomas Kolasa

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