Categories: java, groovy, closures

Groovy GroupBy Variable KeySet

1 answer

I am struggling with using groovy groupBy

I need to support grouping a dataset by a variable key set.

I have written a test to explain my predicament, and would love some help understanding how to implement it:

List<Map> people = [     [         Sex: "Male",         Age: 30,         Job: "Programmer",         Name: "Boris"     ],     [         Sex: "Female",         Age: 30,         Job: "Programmer",         Name: "Jennifer"     ],     [         Sex: "Male",         Age: 40,         Job: "Web Designer",         Name: "Bob"     ],     [         Sex: "Female",         Age: 20,         Job: "Database Admin",         Name: "Alice"     ] ]   List results = [] if(people.groupBy({it.Sex}, {it.Age}) != groupBySpecifiedCols(people, ["Sex", "Age"])){   return "Failed 1" }  if(people.groupBy({it.Sex}, {it.Age}, {it.Job}) != groupBySpecifiedCols(people, ["Sex", "Age", "Job"])){   return "Failed 2" }  def groupBySpecifiedCols(List<Map> data, List<String> columns){   // IMPLEMENT HERE    return null }   return "Success!"​​​​ 

All answers to this question, which has the identifier 61118351

The best answer:

Actually I think I just solved it, after hours of frustration it turned out simple:

def groupBySpecifiedCols(List<Map> data, List<String> columns){   List<Closure> groupByClosures = []   columns.each{ column ->     groupByClosures << { it[column] }   }    return data.groupBy(groupByClosures) } 

EDIT as pointed out in comments, there is a potentially more concise way:

def groupBySpecifiedCols(List<Map> data, List<String> columns){   return data.groupBy(columns.collect{ col -> ((Closure){ it[col] })}) } 

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