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Daily Challenge #210 - Separate Capitalization

dev.to staff on March 21, 2020

Given a string, capitalize the letters that occupy even indexes and odd indexes separately, and return as shown below. Index 0 will be considered e...

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Amin • Mar 21 '20 • Edited

Elm

Note: returning a tuple because returning a List String would mean it can be a list of 0 element as it can be a list of 10, 100, 1000, Infinity elements. Returning a Tuple gives the information to the user that this function will always return two elements in this case, which is suggested by the goal of this challenge. It will be then possible to extract them easily with the Tuple.first & Tuple.second functions.

even : Int -> Bool
even integer =
    modBy 2 integer == 0


odd : Int -> Bool
odd integer =
    not <| even integer


upperIf : ( Int -> Bool ) -> Int -> Char -> Char
upperIf predicate index character =
    if predicate index then
        Char.toUpper character

    else
        character


capitalizeIf : ( Int -> Bool ) -> String -> String
capitalizeIf predicate string =
    string
        |> String.toList
        |> List.indexedMap ( upperIf predicate )
        |> String.fromList


capitalize : String -> ( String, String )
capitalize string =
    ( capitalizeIf even string, capitalizeIf odd string )

@nobody • Mar 21 '20

This is a hallmark of proper functional programming. Elm looks intimidating than more traditional grammars but it's essentially strongly-typed function composition. I love it, and the outer function reads like english.

Amin • Mar 21 '20 • Edited

I won't lie, since this was my first real functional programming language, it was tough, really tough. And this is essentially due to the fact that I was not used to no parens (or not at the same position at least) and function composition mainly.

But functional programming is like a muscle. The best competitors are working hard to obtain a great physical condition. This is the same thing for people like you and me that are used to procedural or oriented-object programming. It requires a lot of practices to get out of our habits.

But when you practiced enough, you'll start to love functional programming and that is the only certainty you have. The rest is up to you. And actually, since I'm a Web Developer, and doing most of my stuff in JavaScript at work (I hope I get to include Elm one day) this has made me a better overall JavaScript developer. There is no time wasted on learning this language, trust me.

Davyd McColl • Mar 21 '20

function capitalize(str) {
  return str.split("").reduce((acc, cur, i) => {
    const 
      odd = i % 2,
      upper = cur.toUpperCase();
    acc[0] += !odd ? upper : cur;
    acc[1] += odd ? upper : cur;
    return acc;
  }, ["", ""]);
}

@nobody • Mar 21 '20

Interesting JS solution....I haven't seen ternary operators used so haphazardly before, I'm not comfortable with them still.

Avalander • Mar 21 '20 • Edited

Scala

A good old fold and I use the Next type to know which side to capitalize next.

sealed trait Next
case object Left extends Next
case object Right extends Next

def capitalize (str: String): (String, String) = {
  val (l, r, _) = str.foldLeft(("", "", Left: Next)) {
    case ((l, r, n), c) => n match {
      case Left  => (l :+ c.toUpper, r :+ c.toLower, Right)
      case Right => (l :+ c.toLower, r :+ c.toUpper, Left)
    }
  }
  (l, r)
}

println(capitalize("abcdef")) // ("AbCdEf", "aBcDeF")

Dian Fay • Mar 23 '20

SQL:

[local] dian#dian= WITH seq AS (
  SELECT regexp_split_to_table('string', '') AS c
), capitalized AS (
  SELECT
    CASE
      WHEN row_number() OVER () % 2 = 0 THEN upper(c)
      ELSE lower(c)
    END AS even,
    CASE
      WHEN row_number() OVER () % 2 = 1 THEN upper(c)
      ELSE lower(c)
    END AS odd
  FROM seq
)
SELECT
  string_agg(even, '') AS even,
  string_agg(odd, '') AS odd
FROM capitalized;
  even  │  odd   
────────┼────────
 sTrInG │ StRiNg
(1 row)

Time: 0.613 ms

Break the string down into a table with one character per row, use the row_number window function to capitalize it each way, then reassemble the final product; the latter two steps can't be combined because window functions can't be nested in aggregate functions.

Craig McIlwrath • Mar 21 '20

Kinda silly solution using 2 mutually recursive functions (Haskell)

import Data.Char (toUpper, toLower) 

skip :: String -> String
skip [] = [] 
skip (c:cs) = c : capitalize' cs

capitalize' :: String -> String
capitalize' [] = [] 
capitalize' (c:cs) = toUpper c : skip cs

capitalize :: String -> (String, String) 
capitalize cs = (capitalize' cs, skip cs)

Avalander • Mar 21 '20

Ooh, clever! I like it!

SavagePixie • Mar 22 '20 • Edited

I'm a bit late to the party, but here's my Elixir solution:

defmodule Letters do
  import Integer, only: [ is_even: 1, is_odd: 1 ]

  def capitalise(str) do
    str
      |> String.split("", trim: true)
      |> Enum.with_index
      |> Enum.map(&_mapper/1)
      |> Enum.unzip
      |> _join
  end

  defp _mapper({ letter, idx })
    when is_even(idx) do
      { String.capitalize(letter), String.downcase(letter) }
    end
  defp _mapper({ letter, idx })
    when is_odd(idx) do
      { String.downcase(letter), String.capitalize(letter) }
    end
  defp _join({ a, b }), do: { Enum.join(a), Enum.join(b) }
end

Ksenia • Mar 28 '20 • Edited

One more Python solution:

def capitalize(s: str) -> list:
    cap_s_even, cap_s_odd = "", ""
    for i in range(0, len(s)):
        if i % 2 == 0:
            cap_s_even+=s[i].upper()
            cap_s_odd+=s[i]
        else:
            cap_s_even+=s[i]
            cap_s_odd+=s[i].upper()
    return [cap_s_even, cap_s_odd]

LordApple • Mar 22 '20

#!/bin/sh

ARR=$(seq 0 $(( ${#1} - 1 )))
LOWER=$(echo "$1" | tr '[:upper:]' '[:lower:]')

for x in $ARR; do 
  (( $x % 2 == 0 )) && ARR_EVEN+=$(echo "${LOWER:$x:1}" | tr '[:lower:]' '[:upper:]') || ARR_EVEN+=$(echo "${LOWER:$x:1}")
  (( $x % 2 )) && ARR_ODD+=$(echo "${LOWER:$x:1}" | tr '[:lower:]' '[:upper:]') || ARR_ODD+=$(echo "${LOWER:$x:1}")
done

echo ${ARR_EVEN[@]} ${ARR_ODD[@]}

Here is some shit I wrote using shellscript

Nilbert • Mar 26 '20

Ruby

method = ->(s) { s.each_char.with_index.map { |c,i| [c.downcase,c.upcase].rotate(i[0])}.transpose.map(&:join)}

method.call 'dev'
=> ["dEv", "DeV"]

method.call 'method'
=> ["mEtHoD", "MeThOd"]

method.call 'hello'
=> ["hElLo", "HeLlO"]

Valts Liepiņš • Mar 22 '20

Solution in Haskell using folding:

import Data.Char (toUpper)

capitalize :: String -> [String]
capitalize str = folder skipCase <$> [("",0),("",1)] <*> pure str
  where
    folder fn init = fst . foldr fn init
    skipCase :: Char -> (String, Int) -> (String, Int)
    skipCase c (cs, i) | i `mod` 2 == 1 = ((toUpper c):cs, i+1)
                       | otherwise      = (c:cs, i+1)

The skipCase folding function takes care of upcasing every 2. letter. The folder is a makes it easier to map the function over both capitalization variations, which then can be applied to the input string.

Jürgen Hermann • Mar 21 '20 • Edited

Any Python version 2.7+.

>>> MiXeD = lambda s: ''.join(x.upper() if i&1==m else x for m in (0,1) for i, x in enumerate(s+' ')).split()
>>> MiXeD('abcdef')
['AbCdEf', 'aBcDeF']

😳 😱

Muhimen • Mar 23 '20

This is the magic of python. Short. I just love it. 💗

Rafael Acioly • Mar 21 '20

If you return like this return _change_even_casing(True), _change_even_casing(False) python will understand that it's already a tuple