I need to store a list of key value pairs. The key value pair will be used by multiple classes, so ideally its something like a list of a structure I define.
Public Structure Person
Public ID As Integer
Public Weight As Decimal
End Structure
'all use Person
class census
class importpeople
class determinebestdiet
etc
I need to sort by value
I need to remove a person (by Person.ID) or add a new key value pair (and re-sort after each add)
I need to sum the total of all values
Seems like often people use dictionaries and then hack around.
You can use List<Person> to help your work
Using the List.Sort method:
theList.Sort(Function(x, y) x.age.CompareTo(y.age))
Using the OrderBy extension method:
theList = theList.OrderBy(Function(x) x.age).ToList()
Details can see this post: https://stackoverflow.com/a/11736001/1050927
Just remove from list and call Sort or OrderBy.
Depends on what you want to do, you can use OrderBy with Skip and Take to get specific nth person after sort.
Just Sum it
PersonList.Sum(Function(per) per.Weight)
And I believe Dictionary can do the same too, just you can't reuse the Person only.
Related
I have a node Country. I know that this node has some properties, but I don't know which. I mean, I know since I've take a look at model. Here is what I've found in documentation:
Country
name: String
iso_2_code: String
iso_3_code: String
region: String
sub.region: String
I know that if I run
MATCH (c:Country)
RETURN c.iso_2_code
I'll get result for one specific property. Is there a query that would as a result return me something like: name, iso_2_code, iso_3_code, region, sub.region?
If I didn't have access to the model how could I list all of the properties that are attached to some node type?
Answering more from a Cypher or openCypher perspective than for a specific implementation. Using the air-routes dataset. There are three things to consider.
Firstly if you know the properties you want, as you mentioned, you can just ask for them explicitly.
MATCH (a:airport {icao:'KDFW'})
RETURN a.city, a.desc
However, if you want all properties, but do not want to list them all, you can just do:
MATCH (a:airport {icao:'KDFW'})
RETURN properties(a)
If you just want the property keys:
MATCH (a:airport {icao:'KDFW'})
RETURN keys(properties(a))
Lastly, if you want the properties plus the label and ID information you can just do:
MATCH (a:airport {icao:'KDFW'})
RETURN a
I have a database called students with columns like so
In my rails model with a scope or function, I would like to select for the single age value based on the id. The id column is unique. So something like
scope :get_age, -> (id) { where(id: id).select(:age) }
However this does not seem to work. I would like for the returned value to just be the int 12. Using something like pluck ends up returning an array which I would like to avoid. How would I go about selecting for just the value of 12?
you know that for one id there is just one row (or no rows) so using where or pluck is not ideal, we want something it returns one row or nothing (find, find_by etc)
def self.get_age(id)
find_by(id: id)&.age
end
some_id = 10
User.get_age(some_id)
Scoping allows you to specify commonly-used queries which can be referenced as method calls on the association objects or models. With these scopes, you can use every method previously covered such as where, joins and includes. All scope bodies should return an ActiveRecord::Relation or nil to allow for further methods (such as other scopes) to be called on it.
Reference: https://guides.rubyonrails.org/active_record_querying.html#scopes
That's why is not working as you expected.
I think the best alternative would be to do as Ursus suggested. Create a method, a query object, etc.
You basically want to read an attribute(age) of your model object. For that, you don't need to write any specific method or scope.
Here is what you can do in the place where you have the id and you want to fetch the age for that record:
object = YourClass.find(id)
object.age
I have two classes.
class A {
String aName;
B b;
public A(String aName, B b) {
this.aName = aName;
this.b = b;
}
public String getaName() {
return aName;
}
public B getB() {
return b;
}
}
class B {
String bName;
public B(String bName) {
this.bName = bName;
}
public String getbName() {
return bName;
}
}
I am storing A as a set in Aerospike and A.aName is primary key. I want a secondary key on A.b. I have created index on A.b attribute and able to persist also. But search from the index is not returning anything. As per my understanding, Aerospike supports only three type of indexes: String, Numeric and Geo,. Is there any option for custom object.
Actually you can also index string, numeric and geo within different source types - basic (meaning just a bin with scalar data), list (so you can index strings or numeric data that is contained in a list), map keys and map values.
See: https://www.aerospike.com/docs/guide/query.html#secondary-index-key-source-type
You could model this in a few ways:
As a map. Let's assume that you store the value of A in a bin whose type is a map, it could have two map-keys - aName and bName. You can build a secondary index for string data on map values. Now, if you search for a specific bName you'll have this record come up.
More rationally you'd do the following as separate bins.
Assume that you use several bins, among them two bins to hold aname and bname. Their values are strings. You could now build a secondary index for string values and a basic index type (string data not contained in a complex data type such as list or map). You'd query for all the records where the predicate is bname = foo.
For a more complex situation one or more bname values map to a single aname, you'd actually model this as a lookup table.
Assume a set (table) called users holding records whose keys are the aname. A single key-value operation such as a read or an upsert works on a specific instance of class A, identified by a given aname. One record in Aerospike per instance of A.
You have another set (table) as the lookup table, where for each unique bname you create a record. The specific bname is the key to this record. The value is the aname. So to find the record in the users set, you first look it up in the lookup table by the bname. You use the value of this record as the key for the users record for that aname. This is the most common way of modeling this type of use case, without a secondary index.
Here is the answer post on Aerospike forum.
Binary blobs can be anything, there’s definitely no way to index that. If there is a particular field in your class you can pull out and set as a separate bin with a string/long type then that would work
https://discuss.aerospike.com/t/secondary-index-on-custom-java-object/6485
Let us consider that I have an IEnumerable(Of IEnumerable(Of Integer)). All the inner IEnumerables contain IDs. I would like to gather all the IDs Distinctly into an IEnumerable(Of Integer). I can do that if I do something like this:
Dim result as New List(Of Integer)
For Each element In IDs
result.AddRange(element)
Next
result = result.Distinct
I have two problems with this approach:
- I have to write the iteration code when there is probably a Function for this purpose that I am unaware of
- The result is a List and I would like to keep the class of the inner IEnumerable
Is there a handy LINQ way to do this?
EDIT:
This question is different from this one, since I am speaking about IEnumerables, not Lists. Yes, I am aware that every List is an IEnumerable, but I am also aware that not every IEnumerable is a List. As a result, this is a more general question than the one which was marked as duplicate, as I have specified in my original question that I would like to maintain the Class of the inner IEnumerable in the result. If it was an array, I prefer to use an array.
You could use SelectMany extension method to flatten the structure, once flatten look for Distinct
result = IDs.SelectMany(Function(x) x).Distinct();
check this Demo
I am using Maps in my code for the first time, hence require some inputs from you experts.
My requirement is I have to check two different tables from database. Value from First table will be used as Key and Value for second table will be used as Value for the key.
Each key will have multiple values, so I will be storing all values against each key in a arraylist i.e. my Map will be like MAP.
Now, my issue is following:
I don't know the total no. of keys, so I can't create arraylist objects in advance. How to manage this?
How can I check if key exists in map such that if it exists then I have to updated the arraylist corresponding to it only. And if it doesn't exist then create new key, create arraylist corresponding to it, populate arraylist with the value.
Finally I have to iterate whole map and use the key and values.
How can it be implemented? Am I following the right approach? if not what is a better approach?
Thanks
With lists in Java you do not need to know the size up front. That is a requirement for Arrays. Therefore just create your Map
Map> myMap = new HashMap<>();
This should work
if (myMap.containsKey(someKey)) {
myMap.get(someKey).add(someValue); // adds a value to the list that already is in the map
} else {
myMap.put(someKey, Arrays.asList(someValue)); // which inserts a new key/value
}
If you need to iterate over all values in the list then you need a nested for loop
for (Map.Entry> entry : myMap.entrySet()) {
// your key = entry.getKey()
for (ValueType value : entry.getValue()) {
// use your value
}
}
http://docs.oracle.com/javase/7/docs/api/java/util/Map.html
Hope that helps.