aggregation

I'm beginning to study OOAD and I'm having difficulty finding a C++ code example that'd illustrate how Association , Aggregation and Composition are implemented programmatically. (There are several posts everywhere but they relate to C# or java). I did find an example or two, but they all conflict with my instructor's instructions and I'm confused. My understanding is that in: Association: Foo has a pointer to Bar object as a data member Aggregation: Foo has a pointer to Bar object and data of Bar is deep copied in that pointer. Composition: Foo has a Bar object as data member. And this is how

Design Pattern by Gamma et al said Consider the distinction between object aggregation and acquaintance and how differently they manifest themselves at compile- and run-times. Aggregation implies that one object owns or is responsible for another object. Generally we speak of an object having or being part of another object. Aggregation implies that an aggregate object and its owner have identical lifetimes. Acquaintance implies that an object merely knows of another object. Sometimes acquaintance is called "association" or the "using" relationship. Acquainted objects may request operations of

I'm new in Core Data, so i want to write simple fetch request to group result by some field and also a count of another field in that group. so for example i have products table i want to retrieve all grouped products by date and the count of product, the simple query in sql is like SELECT DateRegistered,Count(*) FROM Products Group By DateRegistered Your best bet is the very flexible NSFetchedResultsController . You would have a fetch request that simply fetches the Product entity sorted by the date attribute. Please note that core data attributes should start with a small letter. You would

I have a question related to python code. I need to aggregate if the key = kv1, how can I do that? input='num=123-456-7890&kv=1&kv2=12&kv3=0' result={} for pair in input.split('&'): (key,value) = pair.split('=') if key in 'kv1': print value result[key] += int(value) print result['kv1'] Thanks a lot!! I'm assuming you meant key == 'kv1' and also the kv within input was meant to be kv1 and that result is an empty dict that doesn't need result[key] += int(value) just result[key] = int(value) input = 'num=123-456-7890&kv1=1&kv2=12&kv3=0' keys = {k: v for k, v in [i.split('=') for i in input.split(

How is instantiation different from aggregation and from acquaintance? (I have undertood the difference between aggregation and acquaintance, see the quote from the book here ) Instantiation and aggregation seem similar to each other. when object A instantiates or aggregate object B, it seems to me that object A must have a field member referencing object B. Both instantiation and aggregation seem to me not to allow more than one objects to instantiate or aggregate the same object. There might also be other aspects which I miss to consider I have asked What does "a class instantiates another"

I am new to spark scala and I have following situation as below I have a table "TEST_TABLE" on cluster(can be hive table) I am converting that to dataframe as: scala> val testDF = spark.sql("select * from TEST_TABLE limit 10") Now the DF can be viewed as scala> testDF.show() COL1|COL2|COL3 ---------------- abc|abcd|abcdef a|BCBDFG|qddfde MN|1234B678|sd I want an output like below COLUMN_NAME|MAX_LENGTH COL1|3 COL2|8 COL3|6 Is this feasible to do so in spark scala? Plain and simple: import org.apache.spark.sql.functions._ val df = spark.table("TEST_TABLE") df.select(df.columns.map(c => max