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iOS Swift Collections and Control Flow Introduction to Collections Working With Arrays

Posted by Morgan Norelius
Morgan Norelius
682 Points

poorly worded question: concatenate two arrays and rename the resulting expression with the same name as original?

I understand the concept of concatenating two arrays, but I am lost as to how to rename the result the same as one of the originals. It seems like circular logic.

How can a + b = a ?

I found this example on stack overflow: let array1 = [1, 2, 3] let array2 = [4, 5, 6]

let flattenArray = array1 + array2 print(flattenArray) // prints [1, 2, 3, 4, 5, 6]

array.swift 
// Enter your code below
var arrayOfInts: [Int] = [0, 1, 2, 3, 4, 5]
arrayOfInts.append(6)

4 Answers

Jhoan Arango
Jhoan Arango
14,575 Points
Jhoan Arango
Jhoan Arango
14,575 Points

Hello,

This is simple, once you have created an array of Ints that hold six values, you should then re-use the arrayOfInts and concatenate a new array with one value in it. 

var arrayOfInts: [Int] = [1,2,3,4,5,6]

arrayOfInts.append(7) // We use the append method
arrayOfInts = arrayOfInts + [8] // Then we use the arrayOfInts and concatenate a new array with one value in it

Hope this helps

KRIS NIKOLAISEN
KRIS NIKOLAISEN
54,971 Points
KRIS NIKOLAISEN
KRIS NIKOLAISEN
54,971 Points

It wouldn't be a + b = a. It would be a = a + b or shorthand a += b. Keep in mind it is an assignment not an equation.

Shorthand for the challenge might be:

arrayOfInts += [7]
Morgan Norelius
Morgan Norelius
682 Points
Morgan Norelius
Morgan Norelius
682 Points

Thanks. I still struggle with the logic of what seems like a circular reference, but with the guiding of your example, I can accept the idea that the compiler will use the old value of arrayOfInts in the concatenation. I appreciate the help!

KRIS NIKOLAISEN
KRIS NIKOLAISEN
54,971 Points
KRIS NIKOLAISEN
KRIS NIKOLAISEN
54,971 Points

You will see this all the time - especially in loops. What is on the right hand side is evaluated then assigned to the left hand side.

A JavaScript example:

var i;
for (i = 0; i < 10; i++) {
  console.log(i);
}

could also be written:

var i;
for (i = 0; i < 10; i = i + 1) {
  console.log(i);
}

or:

var i;
for (i = 0; i < 10; i += 1) {
  console.log(i);
}
Morgan Norelius
Morgan Norelius
682 Points

Thanks! visualizing the code as "right hand side" and "left hand side" is helpful. Now I understand how a = a + b