🎉 Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io 🎉

# jireton's solution

## to ETL in the Objective-C Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

We are going to do the `Transform` step of an Extract-Transform-Load.

### ETL

Extract-Transform-Load (ETL) is a fancy way of saying, "We have some crufty, legacy data over in this system, and now we need it in this shiny new system over here, so we're going to migrate this."

(Typically, this is followed by, "We're only going to need to run this once." That's then typically followed by much forehead slapping and moaning about how stupid we could possibly be.)

### The goal

We're going to extract some scrabble scores from a legacy system.

The old system stored a list of letters per score:

• 1 point: "A", "E", "I", "O", "U", "L", "N", "R", "S", "T",
• 2 points: "D", "G",
• 3 points: "B", "C", "M", "P",
• 4 points: "F", "H", "V", "W", "Y",
• 5 points: "K",
• 8 points: "J", "X",
• 10 points: "Q", "Z",

The shiny new scrabble system instead stores the score per letter, which makes it much faster and easier to calculate the score for a word. It also stores the letters in lower-case regardless of the case of the input letters:

• "a" is worth 1 point.
• "b" is worth 3 points.
• "c" is worth 3 points.
• "d" is worth 2 points.
• Etc.

Your mission, should you choose to accept it, is to transform the legacy data format to the shiny new format.

### Notes

A final note about scoring, Scrabble is played around the world in a variety of languages, each with its own unique scoring table. For example, an "E" is scored at 2 in the Māori-language version of the game while being scored at 4 in the Hawaiian-language version.

## Setup

There are two different methods of getting set up to run the tests with Objective-C:

• Create an Xcode project with a test target which will run the tests.
• Use the ruby gem `objc` as a test runner utility.

Both are described in more detail here: http://exercism.io/languages/objective-c

### Submitting Exercises

When submitting an exercise, make sure your solution file is in the same directory as the test code.

The submit command will look something like:

``````exercism submit <path-to-exercism-workspace>/objective-c/etl/Etl.m
``````

You can find the Exercism workspace by running `exercism debug` and looking for the line beginning with Workspace.

## Source

The Jumpstart Lab team http://jumpstartlab.com

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### EtlTest.m

``````#import <XCTest/XCTest.h>

#if __has_include("EtlExample.h")
# import "EtlExample.h"
# else
# import "Etl.h"
#endif

NS_ASSUME_NONNULL_BEGIN

typedef NSArray<NSString *> StringArray;

@interface EtlTest : XCTestCase

@end

@implementation EtlTest

- (void)testTransformOneValue {
NSDictionary<NSNumber*, StringArray*  >  *old = @{ @1 : @[ @"W" ] };
NSDictionary<NSString *, NSNumber * > *expected = @{ @"w" : @1 };

NSDictionary<NSString *, NSNumber *> *results = [Etl transform:old];

XCTAssertEqualObjects(expected, results);
}

- (void)testTransformMoreValues {
NSDictionary<NSNumber*, StringArray* > *old = @{ @1 : @[ @"W", @"G" ] };
NSDictionary<NSString *, NSNumber * > *expected = @{ @"w" : @1, @"g" : @1 };

NSDictionary<NSString *, NSNumber *> *results = [Etl transform:old];

XCTAssertEqualObjects(expected, results);
}

- (void)testMoreKeys {
NSDictionary<NSNumber*, StringArray* > *old = @{ @1 : @[ @"A", @"B" ], @2 : @[ @"C", @"D" ] };
NSDictionary<NSString *, NSNumber * > *expected = @{ @"a" : @1, @"b" : @1, @"c" : @2, @"d" : @2 };

NSDictionary<NSString *, NSNumber * > *results = [Etl transform:old];

XCTAssertEqualObjects(expected, results);
}

- (void)testFullDataSet {
NSDictionary<NSNumber*, StringArray* > *old = @{ @1 : @[ @"A", @"E", @"I", @"O", @"U", @"L", @"N", @"R", @"S", @"T" ],
@2 : @[ @"D", @"G" ],
@3 : @[ @"B", @"C", @"M", @"P" ],
@4 : @[ @"F", @"H", @"V", @"W", @"Y" ],
@5 : @[ @"K"],
@8 : @[ @"J", @"X" ],
@10 : @[ @"Q", @"Z" ]
};
NSDictionary<NSString *, NSNumber * > *expected = @{ @"a" : @1, @"b" : @3, @"c" : @3, @"d" : @2, @"e" : @1,
@"f" : @4, @"g" : @2, @"h" : @4, @"i" : @1, @"j" : @8,
@"k" : @5, @"l" : @1, @"m" : @3, @"n" : @1, @"o" : @1,
@"p" : @3, @"q" : @10, @"r" : @1, @"s" : @1, @"t" : @1,
@"u" : @1, @"v" : @4, @"w" : @4, @"x" : @8, @"y" : @4,
@"z" : @10 };

NSDictionary<NSString *, NSNumber * > *results = [Etl transform:old];

XCTAssertEqualObjects(expected, results);

}
@end
NS_ASSUME_NONNULL_END``````
``````//
//  Etl.m
//  Etl
//
//  Created by John Ireton on 5/16/14.
//

#import "Etl.h"

@implementation ETL

+(NSDictionary *)transform:(NSDictionary *)oldDictionary {
NSMutableDictionary *fixedDictionary = [[NSMutableDictionary alloc] init];
for (NSNumber *index in [oldDictionary allKeys]) {
for (NSString *word in oldDictionary[index]) {
[fixedDictionary setObject:index forKey:[word lowercaseString]];
}
}
return fixedDictionary;
}

@end``````

Very nice. If you wanted to use more modern syntax you could also do something like this: NSMutableDictionary *result = [NSMutableDictionary dictionary];

``````for (NSNumber* key in old)
{
for (NSString *charStr in old[key])
{
result[[charStr lowercaseString]] = key;
}
}

return result;
``````

### What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?