Create a custom map/filter/reduce in JavaScript,Python and Ruby

When I learn a new language I like to create my own map/filter/reduce functions in it because is a great way to test my skills, working with functions,arrays,functions as arguments,etc.

So now I will compare how I would create it in all of them starting with JavaScript


// Map

function myMap(array,callback) {
    newArray=[]
    array.forEach(value => newArray.push(callback(value)))
    return newArray
}

const transformed = myMap(["red","blue","purple"] , (color) => `Color ${color}`)

console.log(transformed)

//Filter

function myFilter(array,callback) {
    newArray=[]
    array.forEach(value => callback(value) && newArray.push(value))
    return newArray
}

const filtered = myFilter([1,4,8,2,10,6] , number => number > 5)

console.log(filtered)

// Reduce

function myReduce(array,callback) {
    let acc = 0
    array.forEach(value => acc = callback(acc,value))
    return acc
}

const reduced = myReduce([4,5,9,10] , (acc,current) => acc + current)

console.log(reduced)

Let's do it in python now

python is pretty much the same, just using lambdas instead arrow functions


# Map

def myMap(list,callback):
    newList=[]
    for item in list:
        newList.append(callback(item))
    return newList

transformed=myMap(["red","blue","purple"],lambda color: "Color " + color)

print(transformed)

#Filter

def myFilter(list,callback):
    newList=[]
    for item in list:
        if callback(item) : newList.append(item)
    return newList

filtered= myFilter([1,4,8,2,10,6],lambda number : number>5)

print(filtered)

#Reduce

def myReduce(list,callback):
    acum=0
    for el in list:
        acum=callback(acum,el)
    return acum

reduced = myReduce([4,5,9,10] , lambda current,actual:current+actual)

print(reduced)

And now Ruby

Ruby is a little bit more different, you pass blocks that act like anonymous functions, arguments are enclosed in | argname |
and they are called inside the function using the yield word



#Map

def myMap(array)
    newarray=[]
    for value in array do
        result=yield(value)
        newarray.push(result)
    end
    return newarray
end

transformed=myMap(["red","blue","purple"]) do | color | "Color #{color} " end

puts transformed.inspect

# Filter

def myFilter(array)
    newarray=[]
    for value in array do
        newarray.push(value) if yield(value)
    end
    return newarray
end

filtered = myFilter([1,4,8,2,10,6]) do | number | number > 5 end

puts filtered.inspect


#Reduce

def myReduce(array)
    acc = 0
    for value in array do
        acc = yield(acc,value)
    end
    return acc
end

reduced = myReduce([4,5,9,10]) do | acc,curr | acc+curr end


puts reduced.inspect

Here is a image that show that all of them have the same result

In general I had a lot of fun learning new things and I think it is such a great thing to do to improve your coding skills.

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Create a custom map/filter/reduce in JavaScript,Python and Ruby

ManuelMartinDev

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