How to Convert Pascalcase to Snake_Case

How to convert PascalCase to snake_case?

Try this on for size:

$tests = array(
  'simpleTest' => 'simple_test',
  'easy' => 'easy',
  'HTML' => 'html',
  'simpleXML' => 'simple_xml',
  'PDFLoad' => 'pdf_load',
  'startMIDDLELast' => 'start_middle_last',
  'AString' => 'a_string',
  'Some4Numbers234' => 'some4_numbers234',
  'TEST123String' => 'test123_string',
);

foreach ($tests as $test => $result) {
  $output = from_camel_case($test);
  if ($output === $result) {
    echo "Pass: $test => $result\n";
  } else {
    echo "Fail: $test => $result [$output]\n";
  }
}

function from_camel_case($input) {
  preg_match_all('!([A-Z][A-Z0-9]*(?=$|[A-Z][a-z0-9])|[A-Za-z][a-z0-9]+)!', $input, $matches);
  $ret = $matches[0];
  foreach ($ret as &$match) {
    $match = $match == strtoupper($match) ? strtolower($match) : lcfirst($match);
  }
  return implode('_', $ret);
}

Output:

Pass: simpleTest => simple_test
Pass: easy => easy
Pass: HTML => html
Pass: simpleXML => simple_xml
Pass: PDFLoad => pdf_load
Pass: startMIDDLELast => start_middle_last
Pass: AString => a_string
Pass: Some4Numbers234 => some4_numbers234
Pass: TEST123String => test123_string

This implements the following rules:

1. A sequence beginning with a lowercase letter must be followed by lowercase letters and digits;
2. A sequence beginning with an uppercase letter can be followed by either:
   
   
   • one or more uppercase letters and digits (followed by either the end of the string or an uppercase letter followed by a lowercase letter or digit ie the start of the next sequence); or
   • one or more lowercase letters or digits.

Javascript convert PascalCase to underscore_case/snake_case

You could try the below steps.

• Capture all the uppercase letters and also match the preceding optional dot character.

• Then convert the captured uppercase letters to lowercase and then return back to replace function with an _ as preceding character. This will be achieved by using anonymous function in the replacement part.

• This would replace the starting uppercase letter to _ + lowercase_letter.

• Finally removing the starting underscore will give you the desired output.

  var s = 'TypeOfData.AlphaBeta';
  console.log(s.replace(/(?:^|\.?)([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));
  

OR

var s = 'TypeOfData.AlphaBeta';alert(s.replace(/\.?([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));

How to convert PascalCase to snake_case?

Try this on for size:

$tests = array(
  'simpleTest' => 'simple_test',
  'easy' => 'easy',
  'HTML' => 'html',
  'simpleXML' => 'simple_xml',
  'PDFLoad' => 'pdf_load',
  'startMIDDLELast' => 'start_middle_last',
  'AString' => 'a_string',
  'Some4Numbers234' => 'some4_numbers234',
  'TEST123String' => 'test123_string',
);

foreach ($tests as $test => $result) {
  $output = from_camel_case($test);
  if ($output === $result) {
    echo "Pass: $test => $result\n";
  } else {
    echo "Fail: $test => $result [$output]\n";
  }
}

function from_camel_case($input) {
  preg_match_all('!([A-Z][A-Z0-9]*(?=$|[A-Z][a-z0-9])|[A-Za-z][a-z0-9]+)!', $input, $matches);
  $ret = $matches[0];
  foreach ($ret as &$match) {
    $match = $match == strtoupper($match) ? strtolower($match) : lcfirst($match);
  }
  return implode('_', $ret);
}

Output:

Pass: simpleTest => simple_test
Pass: easy => easy
Pass: HTML => html
Pass: simpleXML => simple_xml
Pass: PDFLoad => pdf_load
Pass: startMIDDLELast => start_middle_last
Pass: AString => a_string
Pass: Some4Numbers234 => some4_numbers234
Pass: TEST123String => test123_string

This implements the following rules:

1. A sequence beginning with a lowercase letter must be followed by lowercase letters and digits;
2. A sequence beginning with an uppercase letter can be followed by either:
   
   
   • one or more uppercase letters and digits (followed by either the end of the string or an uppercase letter followed by a lowercase letter or digit ie the start of the next sequence); or
   • one or more lowercase letters or digits.

How to convert Camel case string to snake case

Try this,

import (
    "fmt"
    "strings"
    "regexp"
)

var matchFirstCap = regexp.MustCompile("(.)([A-Z][a-z]+)")
var matchAllCap   = regexp.MustCompile("([a-z0-9])([A-Z])")

func ToSnakeCase(str string) string {
    snake := matchFirstCap.ReplaceAllString(str, "${1}_${2}")
    snake  = matchAllCap.ReplaceAllString(snake, "${1}_${2}")
    return strings.ToLower(snake)
}

Run:

func main() {   
    fmt.Println(ToSnakeCase("IGotInternAtGeeksForGeeks"))
}

Output:

i_got_intern_at_geeks_for_geeks

NOTE: This will not work for many non-English languages.

How to convert camelcase to snake case in Javascript?

const camelToSnakeCase = str => str.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`);

Change the values in a column from PascalCase to snake_case using SQL

You should be able to use REGEXP_REPLACE to insert an underscore between a lower-case character followed by an upper-case character, and then LOWER to convert to lower case i.e.

SELECT LOWER(REGEXP_REPLACE(fieldname, '([a-z])([A-Z])', '\\1_\\2'))
FROM yourtable

Elegant Python function to convert CamelCase to snake_case?

Camel case to snake case

import re

name = 'CamelCaseName'
name = re.sub(r'(?<!^)(?=[A-Z])', '_', name).lower()
print(name)  # camel_case_name

If you do this many times and the above is slow, compile the regex beforehand:

pattern = re.compile(r'(?<!^)(?=[A-Z])')
name = pattern.sub('_', name).lower()

To handle more advanced cases specially (this is not reversible anymore):

def camel_to_snake(name):
    name = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', name).lower()

print(camel_to_snake('camel2_camel2_case'))  # camel2_camel2_case
print(camel_to_snake('getHTTPResponseCode'))  # get_http_response_code
print(camel_to_snake('HTTPResponseCodeXYZ'))  # http_response_code_xyz

To add also cases with two underscores or more:

def to_snake_case(name):
    name = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
    name = re.sub('__([A-Z])', r'_\1', name)
    name = re.sub('([a-z0-9])([A-Z])', r'\1_\2', name)
    return name.lower()

Snake case to pascal case

name = 'snake_case_name'
name = ''.join(word.title() for word in name.split('_'))
print(name)  # SnakeCaseName

Javascript method for changing snake_case to PascalCase

This should do the trick.

function _snake2Pascal( str ){
    str +='';
    str = str.split('_');
    for(var i=0;i<str.length;i++){ 
        str[i] = str[i].slice(0,1).toUpperCase() + str[i].slice(1,str[i].length);
    }
    return str.join('');
}

edit:

a version that passes all your test cases shown in the OP:

function snake2Pascal( str ){
    str +='';
    str = str.split('_');

    function upper( str ){
        return str.slice(0,1).toUpperCase() + str.slice(1,str.length);
    }

    for(var i=0;i<str.length;i++){
        var str2 = str[i].split('/');
        for(var j=0;j<str2.length;j++){
            str2[j] = upper(str2[j]);
        }
        str[i] = str2.join('');
    }
    return str.join('');
}

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