regex switch

function ProteinTranslation {
    [CmdletBinding()]
    Param(
        [string]$Strand
    )
    $codons = $Strand -split "(\w{3})" -ne ""
    switch -Regex ($codons) {
        "AUG"           { "Methionine" }
        "UU[U|C]"       { "Phenylalanine" }
        "UU[A|G]"       { "Leucine" }
        "UC[U|C|A|G]"   { "Serine" }
        "UA[U|C]"       { "Tyrosine" }
        "UG[U|C]"       { "Cysteine" }
        "UGG"           { "Tryptophan" }
        "(UAA|UAG|UGA)" { break }
        Default {Throw "Error: Invalid codon"}
    }
}

This approach utilize regex and switch statement to work with strings.

First, the string being split into an array of strings by length 3. When a string length is not divisible by 3, the last string will simply be a string of lenght less than 3.

$codons = $Strand -split "(\w{3})" -ne ""

Next we utilize the flexibility of switch statement in Powershell to translate these strings of codons into the correct protein name. We set the -Regex flag for switch statement so it can match regex patterns of codons to correspondent proteins.

switch -Regex ($codons) {
        "AUG"           { "Methionine" }
        "UU[U|C]"       { "Phenylalanine" }
        "UU[A|G]"       { "Leucine" }
        "UC[U|C|A|G]"   { "Serine" }
        "UA[U|C]"       { "Tyrosine" }
        "UG[U|C]"       { "Cysteine" }
        "UGG"           { "Tryptophan" }

If the codon match any of three terminating codons (STOP value) then we simply just break out of the switch statement, and end the translation there.

        "(UAA|UAG|UGA)" { break }

Anything else and it would be an invalid codon and should throw an error.

        Default {Throw "Error: Invalid codon"}

If no error were thrown, an array of proteins is now being returned.

Regular expression.

Switch statement.