collect (defined on TraversableLike and available in all subclasses) works with a collection and a PartialFunction. It also just so happens that a bunch of case clauses defined inside braces are a partial function (See section 8.5 of the Scala Language Specification [warning – PDF]) As in exception handling: try { … do something risky … Read more
You can do this with a lambda: extract_keyname = ->(h) { h[:keyname] } ary_of_hashes.map(&extract_keyname) This tends to be more useful if the block’s logic is more complicated than simply extracting a value from a Hash. Also, attaching names to your bits of logic can help clarify what a chain of Enumerable method calls is trying … Read more
Not maintaining the order is a property of the Map that stores the result. If you need a specific Map behavior, you need to request a particular Map implementation. E.g. LinkedHashMap maintains the insertion order: groupedResult = people.collect(Collectors.groupingBy( p -> new GroupingKey(p, groupByColumns), LinkedHashMap::new, Collectors.mapping((Map<String, Object> p) -> p, toList()))); By the way, there is … Read more
Unfortunately, the error message “Non-static method cannot be refered from a static context.” is just a place-holder for any type mismatch problem, when method references are involved. The compiler simply failed to determine the actual problem. In your code, the target type Map<Integer, Map<String, List<String>>> doesn’t match the result type of the combined collector which … Read more
Array#each takes an array and applies the given block over all items. It doesn’t affect the array or creates a new object. It is just a way of looping over items. Also it returns self. arr=[1,2,3,4] arr.each {|x| puts x*2} Prints 2,4,6,8 and returns [1,2,3,4] no matter what Array#collect is same as Array#map and it … Read more
First, if you are using ruby < 1.9: array = [ {:price => 1, :count => 3}, {:price => 2, :count => 3}, {:price => 3, :count => 3} ] Then to get what you need: array.map{|x| x[:price]}
You need to use agg. Example: from pyspark import SparkContext from pyspark.sql import HiveContext from pyspark.sql import functions as F sc = SparkContext(“local”) sqlContext = HiveContext(sc) df = sqlContext.createDataFrame([ (“a”, None, None), (“a”, “code1”, None), (“a”, “code2”, “name2”), ], [“id”, “code”, “name”]) df.show() +—+—–+—–+ | id| code| name| +—+—–+—–+ | a| null| null| | a|code1| … Read more
With dplyr >= 0.7.0, you can use pull() to get a vector from a tbl. library(dplyr, warn.conflicts = FALSE) db <- src_sqlite(tempfile(), create = TRUE) iris2 <- copy_to(db, iris) vec <- pull(iris2, Species) head(vec) #> [1] “setosa” “setosa” “setosa” “setosa” “setosa” “setosa”
There’s no difference, in fact map is implemented in C as rb_ary_collect and enum_collect (eg. there is a difference between map on an array and on any other enum, but no difference between map and collect). Why do both map and collect exist in Ruby? The map function has many naming conventions in different languages. … Read more