Kotlin - A Brain-Friendly Guide Ch12

1. Built-in
higher-order functions
Kotlin Study Group #3
Andy Lu
2021.06.17

2. Who am I
Andy Lu
Android Engineer in FutureDial
第二屆 Kotlin 讀書會導讀者
❤ Kotlin
❤ Flutter
Medium: https://medium.com/@andyludeveloper
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3. Agenda
● Recap higher-order fuction
● Built-in higher-order functions
● Functional programming
● Q&A
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4. Recap higher-order function
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5. What’s higher-order function?
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6. What’s higher-order function?
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Function as
arguments
(one or more)

7. What’s higher-order function?
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Function as
arguments
(one or more)
Returns
function as a
results.

8. Why higher-order function?
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9. Why higher-order function?
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No temporary variables

10. Why higher-order function?
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No temporary variables
Function call chaining

11. Why higher-order function?
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No temporary variables
Function call chaining
Higher level of abstraction

12. How to use higher-order function?
Ex: { a, b -> a+b }
● { }
● Parameters (a, b)
● Body (after ->)
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13. Built-in higher-order functions
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14. minBy, maxBy
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15. minByOrNull
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16. maxByOrNull
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17. Thinking
How to find the oldest child?
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18. Use maxByOrNull
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19. sumBy, sumByDouble
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20. sumBy
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21. sumByDouble
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22. Thinking
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How to calculate all the donate?

23. Use sumBy
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24. Use for-loop
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Temporary variable

25. filter
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26. filter
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Predicate
Filtered list
● Filtered new list

27. filter
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[“three”, “four”]

28. Family of filter
● filter
● filterTo
● filterNot
● filterIndexed
● ...
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29. map
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30. map
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● Collection transformation.
● Build new collection
For each subsequent element

31. map
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[6, 12, 18, 24]

32. Family of map
● map
● mapNotNull
● mapKeys
● mapValues
● mapIndexed
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33. forEach
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34. forEach
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● for-loop like
● Support function call chaining
● No return value

35. forEach - V.S for-loop
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36. Function call chaining
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37. Function call chaining
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38. Closure
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39. groupBy
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40. groupBy
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● Grouping collection elements

41. groupBy
{3=[one, two], 5=[three], 4=[four]}
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42. fold
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43. fold
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● Operator and accmulate result

44. fold
20
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45. Functional Programming
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46. Three types of functions
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Transform
map zip
flatten ...
Filter
filter
partition
...
Combine
fold
reduce
max
sum
...

47. Q & A
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