How to convert a list of String lists to a list of objects in Scala?

Question

I'm reading a .csv file that returns a list of String lists, recipiesList, in the following format:

List(List(Portuguese Green Soup, Portugal), List(Grilled Sardines, Portugal), List(Salted Cod with Cream, Portugal))

I have a class Recipe, which has been defined in the following manner:

case class Recipe(name: String, country: String)

Is there any immediate way that I can transform recipiesList into a list of type List[Recipe]? Such as with map or some sort of extractor?

Jesper · Accepted Answer · 2017-05-11 20:46:01Z

6

You can transform elements of a List using the map method:

val input = List(List("Portuguese Green Soup", "Portugal"),
    List("Grilled Sardines", "Portugal"),
    List("Salted Cod with Cream", "Portugal"))

val output = input map { case List(name, country) => Recipe(name, country) }

answered May 11, 2017 at 20:46

Jesper

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5 Comments

Cyrille Corpet Over a year ago

It's safer to use collect instead of map when the given function is partial. That way, if your data is corrupt (say some element in input as three elements for some reason), it will simply be ignored, rather than throwing a MatchError.

The Archetypal Paul Over a year ago

@CyrilleCorpet, if my team start writing code that silently ignores errors in the input, I'll be having words! Better to use a case _ and do something with the errors

Cyrille Corpet Over a year ago

@TheArchetypalPaul, I'd rather silently ignore them than let them break my production app. My main point was that map with a partial function is not pure, it introduces (probably) unexpected errors, and should be avoided, when possible.

The Archetypal Paul Over a year ago

@CyrilleCorpet " I'd rather silently ignore them than let them break my production app" False dichotomy. You don't have to ignore them to avoid breaking the app

Cyrille Corpet Over a year ago

@TheArchetypalPaul I completely agree with you. But using map with only the expected case will break the app on unexpected cases. I like your idea with case _ which makes the function total, I just try to alert on the fact that you should not use a partial function where a total one is expected. In fact, if it where a sealed trait instead of List[String] as input type, the scala compiler itself would issue a warning.

Assaf Mendelson · Accepted Answer · 2017-05-11 20:45:59Z

3

The quick way would be:

recipiesList.map(s => Recipe(s(0), s(1))

answered May 11, 2017 at 20:45

Assaf Mendelson

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