Ion - Playing with Records - Part Two

   
   
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Article Series

This article series discuss more than 30 different programming languages. Please read overview before you read any of the details.

Playing with Records Related Articles.

Table of Content
Where to Discuss?

Local Group

Preface

Goal: Exploring Ion Shell for string processing.

4: Approach in Solving Unique

A custom example, that you can rewrite.

An Algorithm Case

Why reinvent the wheel?

The same reason as other article.

x:xs Pattern Matching

The same with other article as well.

Exclude Function

Consider array in code below:

let tags:[str] = [ \
  "60s" "jazz" "60s" "rock" \
  "70s" "rock" "70s" "pop" ]

The exclude function is just a filter. ion shell has this \\= operator to diff array.

fn exclude value:str tags:[str]
  let tags \\= [$value]
  echo @tags
end

Finally we can call them in main script. and reformat the output using fish.

let tags_ex = [@(exclude "rock" [@tags])]
echo $join(@tags_ex :)

With the result as below array:

❯ ./11-exclude.sh
60s:jazz:60s:70s:70s:pop

Ion Shell: Exclude Function

The ion script looks tidier than bash.

Recursive Unique Function

With exclude function above, we can build unique function recursively, as below code:

#!/usr/bin/env ion

fn unique tags:[str]
  if test $len(@tags) -le 1
    echo @tags
  else
    let head =  @tags[0]
    let tail = [@tags[1..=$len(@tags)]]

    let tail \\= [$head]
    let uniq = [ @(unique [@tail]) ]

    echo [ [$head] @uniq ]
  end
end

Ion Shell: The Unique Function

We can also get rid of exclude function, by using the //= operator.

Applying Unique to Simple Array

Now we can apply the method to our unique song challenge.

#!/usr/bin/env ion

let tags:[str] = [ \
  "60s" "jazz" "60s" "rock" \
  "70s" "rock" "70s" "pop" ]

fn exclude value:str tags:[str]
  let tags \\= [$value]
  echo @tags
end

fn unique tags:[str]
  if test $len(@tags) -le 1
    echo @tags
  else
    let head =  @tags[0]
    let tail = [@tags[1..=$len(@tags)]]

    let xcld = [ @(exclude $head [@tail]) ]
    let uniq = [ @(unique [@xcld]) ]

    echo [ [$head] @uniq ]
  end
end

echo $join(@(unique [@tags]) :)

With the same result as below

Ion Shell: Solving Unique Song

With the result as below array:

❯ ./12-unique-a.sh
60s:jazz:rock:70s:pop

Applying Unique to data Structure

We can also apply the method to our unique song challenge.

#!/usr/bin/env ion
source ./MySongs.sh
source ./MyHelperFlatten.sh
source ./MyHelperUnique.sh

# Extract flatten output to array
let tags_nl = $(flatten [@songs])
let tags    = [@split($tags_nl \n)]
echo $join(@(unique [@tags]) :)

With the result as below array:

❯ ./12-unique-b.sh
60s:jazz:rock:70s:pop

Ion shell: Solving Unique Song

What is Next 🤔?

Consider continue reading [ JQ in Bash - Playing with Records ].