LINQ with Dictionary

Protein Translation
Protein Translation in C# 
using System;
using System.Collections.Generic;
using System.Linq;

public static class ProteinTranslation
{

    private static readonly IDictionary<string, string> proteins = new Dictionary<string, string>();

    static ProteinTranslation()
    {
          proteins.Add("AUG", "Methionine");
          proteins.Add("UUU", "Phenylalanine");
          proteins.Add("UUC" , "Phenylalanine");
          proteins.Add("UUA", "Leucine");
          proteins.Add("UUG" , "Leucine");
          proteins.Add("UCU", "Serine");
          proteins.Add("UCC", "Serine");
          proteins.Add("UCA", "Serine");
          proteins.Add("UCG", "Serine");
          proteins.Add("UAU", "Tyrosine");
          proteins.Add("UAC", "Tyrosine");
          proteins.Add("UGU", "Cysteine");
          proteins.Add("UGC", "Cysteine");
          proteins.Add("UGG", "Tryptophan");
          proteins.Add("UAA", "STOP");
          proteins.Add("UAG", "STOP");
          proteins.Add("UGA", "STOP");
    }
    
    public static string[] Proteins(string strand)
    {
        return strand
            .Select((_, i) => i)
            .Where(i => i % 3 == 0)
            .Select(i =>  proteins[strand.Substring(i, 3)])
            .TakeWhile(protein => protein != "STOP")
            .ToArray();
    }
 
}

The approach begins by defining a private, static, readonly Dictionary for translating the codons to proteins. It is private because it isn't needed outside the class. It is static because only one is needed to serve every instance of the class. It is readonly because, although it has interior mutability (meaning its elements can change), the Dictionary variable itself will not be assigned to another Dictionary.

The static constructor loads the Dictionary from the codons and their matching protein.

The Proteins() method starts by calling the LINQ Select() method to iterate the characters of the input strand. Inside the body of the Select() is a lambda function that take two arguments: the character and its index. Since the character isn't used, it is represented by a discard (_).

The index from Select() is chained into the input for the Where() method, which filters the indexes by whether they are evenly divisible by 3.

The surviving indexes are chained into the input for the next Select(). Inside the body of the Select() is a lambda which calls the Substring() method, passing the index for the starting position and a length of 3. For a strand of six characters, the first surviving index will be 0, since 0 divided by 3 has a remainder of 0, and the Substring() will get the characters from positions 0 through 2. The next surviving index will be 3, since 3 divided by 3 has a remainder of 0, and the Substring() will get the characters from positions 3 through 5. These substrings are the codons that are used as the key to lookup their matching proteins in the Dictionary.

Each matching protein is chained from the output of Select() to the input of the TakeWhile() method, which filters the proteins in a lambda based on whether the protein is a STOP codon. Unlike Where(), once the lambda in TakeWhile() encounters a failing lambda condition, it does not continue to iterate, but stops.

The proteins that survive the TakeWhile() are chained into the input of the ToArray() method.

The ToArray() method is used to return an array of the matched proteins from the Proteins() method.

6th Nov 2024 · Found it useful?

Other Approaches to Protein Translation in C#

Other ways our community solved this exercise
while (endIndex <= length)
{
    var codon = strand.Substring(endIndex - 3, 3);
    var protein = lookup[codon];
    switch (protein)
    {
        case "STOP":
            return proteins.ToArray();
Substring with Dictionary

Iterate Substrings with Dictionary. 

while (endIndex <= length)
{
    var codon = strand.Substring(endIndex - 3, 3);
    var protein = ToProtein(codon);
    switch (protein)
    {
        case "STOP":
            return proteins.ToArray();
Switch on a tuple

Iterate Substrings with switch. 

public static string[] Proteins(string strand) =>
    strand.Chunked(3).Select(codon => proteins[codon]).TakeWhile(protein => protein != "STOP").ToArray();

private static IEnumerable<string> Chunked(this string input, int size)
{
    for (var i = 0; i < input.Length; i += size)
        yield return input[i..(i + size)];
}
yield with Dictionary

Iterate using yield with Dictionary. 

public static string[] Proteins(string strand) =>
   strand.Chunked(3).Select(ToProtein).TakeWhile(protein => protein != "STOP").ToArray();

private static IEnumerable<string> Chunked(this string input, int size)
{
    for (var i = 0; i < input.Length; i += size)
        yield return input[i .. (i + size)];
}
yield with switch

Iterate using yield with switch.