How can I sort a collection by two criteria in Cincom VisualWorks?
Example: I have an OrderedCollection that contains persons, and want a new collection that sort the persons first by age, and then if the age is the same sort the persons by name.
Hope you can understand my english! Thanks..
Sean's code is fine, but I prefer it written this way, which is more intention-revealing and slightly more efficient:
people sort: [ :a :b |
a age < b age
or: [a age = b age and: [ a name < b name ] ]
The idea is that the sort block should answer true if item a sorts before item b. With two keys to consider, an item sorts before another item if either its primary key (age) is less, or the primary key is the same, and the secondary key (name) is less.
This translate directly into the code above, and can be easily extended to a third or more sort criteria (e.g., either the secondary key is less, or it is the same and the tertiary key is less).
Travis Griggs implemented an interesting way of doing this kind of sort in a much more succinct way. He published his work as TAG-SortFunctions in the Cincom Public Repository, and I believe it has been integrated into the next release of VisualWorks. See his blog post on the topic and the followup for details. Using this package, you would simply write something like this (untested):
people sort: #age sortUp, #name sortUp
people sort: [ :a :b |
a age = b age
ifTrue: [ a name < b name ]
ifFalse: [ a age < b age ] ]
What Randy said, but it is integrated in VisualWorks 7.8, and the syntax would be
aCollection asSortedCollection: #age ascending, #name descending
where you can also use sort:, or anything else that would take a sortBlock.
Related
I am relatively new to coding and am learning ruby right now. I came across a problem where I have a huge data record (>100k record) consisting of unique ID and another consisting of the date of birth. So it's basically a 2D array. How do I go about creating a method such that every time when I key in method(year), it will give me all the unique ID of those born in the year i choose? And how do I loop this?
The method I tried doing is as follow:
def Id_with_year(year)
emPloyee_ID_for_searching_year = [ ]
employeelist.sort_by!{|a,b|b}
if employeelist.select{|a,b| b == year}.map{|a,b| a}
return emPloyee_ID_for_searching_year
end
end
I should point out that the ID are sorted. That's why I am trying to sort the year in this method so that it will give me all the ID for the year I key in. The output I had was that it returned me [ ] with nothing inside instead of the ID.
Sidenote: methods in ruby are to be named in snake case (this is not mandatory, though.)
The problem you experience is you return what was never changed. The below should work:
def id_with_year(year)
employeelist.sort_by(&:last) # sorting by last element of array
.select{|_,b| b == year} # select
.map(&:first) # map to the first element
end
Let's suppose a store owner wants to know how well his products are selling around the world, and which are selling best where.
He has the following data: |ID,Currency,Quantity,Location|
Rather than iterate through the data for each currency (data set > 10,000), is there a way to put the data into arrays specific to the currency without explicit designation...i.e., is there a way to avoid
if curr == "USD"; USDid << ID; USDquan << Quantity
elsif...
...and so on? For the purposes of this question, assume the *id and *quan arrays exist for the currencies under observation.
Is there some sort of regex trick that can look at the currency and put the data in the appropriate arrays?
Yes. Use a hash of arrays instead of multiple arrays:
sale_data = {}
sale_data.default = {"ID" => [], "Quantity" => [], "Location" => []}
# Later...
sale_data[curr]["ID"] << ID; sale_data[curr]["Quantity"] << quan; #Etc..
The default= call makes it so you can just assign as many currencies as you want without every predefining them. So, anywhere in your code, if there are not prior entries for, say, USD, when you add data, one is created.
I have two arrays and I want to see the total number of matches, between the arrays individual items that their are.
For example arrays with:
1 -- House, Dog, Cat, Car
2 -- Cat, Book, Box, Car
Would return 2.
Any ideas? Thanks!
EDIT/
Basically I have two forms (for two different types of users) that uses nested attributes to store the number of skills they have. I can print out the skills via
current_user.skills.each do |skill| skill.name
other_user.skills.each do |skill| skill.name
When I print out the array, I get: #<Skill:0x1037e4948>#<Skill:0x1037e2800>#<Skill:0x1037e21e8>#<Skill:0x1037e1090>#<Skill:0x1037e0848>
So, yes, I want to compare the two users skills and return the number that match. Thanks for your help.
This works:
a = %w{house dog cat car}
b = %w{cat book box car}
(a & b).size
Documentation: http://www.ruby-doc.org/core/classes/Array.html#M000274
To convert classes to an array using the name, try something like:
class X
def name
"name"
end
end
a = [X.new]
b = [X.new]
(a.map{|x| x.name} & b.map{|x| x.name}).size
In your example, a is current_user.skills and b is other_users.skills. x is simply a reference to the current index of the array as the map action loops through the array. The action is documented in the link I provided.
after fiddling around with dictionaries, I came to the conclusion, that I would need a data structure that would allow me an n to n lookup. One example would be: A course can be visited by several students and each student can visit several courses.
What would be the most pythonic way to achieve this? It wont be more than 500 Students and 100 courses, to stay with the example. So I would like to avoid using a real database software.
Thanks!
Since your working set is small, I don't think it is a problem to just store the student IDs as lists in the Course class. Finding students in a class would be as simple as doing
course.studentIDs
To find courses a student is in, just iterate over the courses and find the ID:
studentIDToGet = "johnsmith001"
studentsCourses = list()
for course in courses:
if studentIDToGet in course.studentIDs:
studentsCourses.append(course.id)
There's other ways you could do it. You could have a dictionary of studentIDs mapped to courseIDs or two dictionaries that - one mapped studentIDs:courseIDs and another courseIDs:studentIDs - when updated, update each other.
The implementation I wrote out the code for would probably be the slowest, which is why I mentioned that your working set is small enough that it would not be a problem. The other implentations I mentioned but did not show the code for would require some more code to make them work that just aren't worth the effort.
It depends completely on what operations you want the structure to be able to carry out quickly.
If you want to be able to quickly look up properties related to both a course and a student, for example how many hours a student has spent on studies for a specific course, or what grade the student has in the course if he has finished it, and if he has finished it etc. a vector containing n*m elements is probably what you need, where n is the number of students and m is the number of courses.
If on the other hand the average number of courses a student has taken is much less than the total number of courses (which it probably is for a real case scenario), and you want to be able to quickly look up all the courses a student has taken, you probably want to use an array consisting of n lists, either linked lists, resizable vectors or similar – depending on if you want to be able to with the lists; maybe that is to quickly remove elements in the middle of the lists, or quickly access an element at a random location. If you both want to be able to quickly remove elements in the middle of the lists and have quick random access to list elements, then maybe some kind of tree structure would be the most suitable for you.
Most tree data structures carry out all basic operations in logarithmic time to the number of elements in the tree. Beware that some tree data structures have an amortized time on these operators that is linear to the number of elements in the tree, even though the average time for a randomly constructed tree would be logarithmic. A typical example of when this happens is if you use a binary search tree and build it up with increasingly large elements. Don't do that; scramble the elements before you use them to build up the tree in that case, or use a divide-and-conquer method and split the list in two parts and one pivot element and create the tree root with the pivot element, then recursively create trees from both the left part of the list and the right part of the list, these also using the divide-and-conquer method, and attach them to the root as the left child and the right child respectively.
I'm sorry, I don't know python so I don't know what data structures that are part of the language and which you have to create yourself.
I assume you want to index both the Students and Courses. Otherwise you can easily make a list of tuples to store all Student,Course combinations: [ (St1, Crs1), (St1, Crs2) .. (St2, Crs1) ... (Sti, Crsi) ... ] and then do a linear lookup everytime you need to. For upto 500 students this ain't bad either.
However if you'd like to have a quick lookup either way, there is no builtin data structure. You can simple use two dictionaries:
courses = { crs1: [ st1, st2, st3 ], crs2: [ st_i, st_j, st_k] ... }
students = { st1: [ crs1, crs2, crs3 ], st2: [ crs_i, crs_j, crs_k] ... }
For a given student s, looking up courses is now students[s]; and for a given course c, looking up students is courses[c].
For something simple like what you want to do, you could create a simple class with data members and methods to maintain them and keep them consistent with each other. For this problem two dictionaries would be needed. One keyed by student name (or id) that keeps track of the courses each is taking, and another that keeps track of which students are in each class.
defaultdicts from the 'collections' module could be used instead of plain dicts to make things more convenient. Here's what I mean:
from collections import defaultdict
class Enrollment(object):
def __init__(self):
self.students = defaultdict(set)
self.courses = defaultdict(set)
def clear(self):
self.students.clear()
self.courses.clear()
def enroll(self, student, course):
if student not in self.courses[course]:
self.students[student].add(course)
self.courses[course].add(student)
def drop(self, course, student):
if student in self.courses[course]:
self.students[student].remove(course)
self.courses[course].remove(student)
# remove student if they are not taking any other courses
if len(self.students[student]) == 0:
del self.students[student]
def display_course_enrollments(self):
print "Class Enrollments:"
for course in self.courses:
print ' course:', course,
print ' ', [student for student in self.courses[course]]
def display_student_enrollments(self):
print "Student Enrollments:"
for student in self.students:
print ' student', student,
print ' ', [course for course in self.students[student]]
if __name__=='__main__':
school = Enrollment()
school.enroll('john smith', 'biology 101')
school.enroll('mary brown', 'biology 101')
school.enroll('bob jones', 'calculus 202')
school.display_course_enrollments()
print
school.display_student_enrollments()
school.drop('biology 101', 'mary brown')
print
print 'After mary brown drops biology 101:'
print
school.display_course_enrollments()
print
school.display_student_enrollments()
Which when run produces the following output:
Class Enrollments:
course: calculus 202 ['bob jones']
course: biology 101 ['mary brown', 'john smith']
Student Enrollments:
student bob jones ['calculus 202']
student mary brown ['biology 101']
student john smith ['biology 101']
After mary brown drops biology 101:
Class Enrollments:
course: calculus 202 ['bob jones']
course: biology 101 ['john smith']
Student Enrollments:
student bob jones ['calculus 202']
student john smith ['biology 101']
This is what I have so far
ages = [20,19,21,17,31,33,34]
names = [Bob, Bill, Jill, Aimee, Joe, Matt, Chris]
How do I take ages and apply a method to it to extract the largest integer out of it and learn its indexed position. The reason being I want to know which person in names is the oldest. Parallel assignment is blocking my ability to do a .sort on the array becasue it changes the position of element associted with names.
Please include code to mull over thanks,
ages.zip(names).max
names[ages.index(ages.max)]
What it does is find the maximum value in ages (ages.max), get the index of the first matching value in ages, and use it to get the corresponding person. Note that if two or more people have the same age which is the maximum, it'll only give you the name of the first one in the array.
Edit: To address your comment, I'm not sure why you need this parallel arrays structure (it'd be much easier if you just had a person object). Nevertheless, you can try something like:
indices = []
ages.each_with_index { |age, i| indices << i if age < 20 }
indices.each { |i| puts names[i] }