Is there a real unique ID for a Video on a YouTube playlist? YouTube offers a playlistItem.id and tells us that this ID is...
The ID that YouTube uses to uniquely identify the playlist item
What I've found out is that this ID is the ID of the Position of a PlaylistItem within a Playlist. If you delete your one and only video on a playlist and you put another video on your playlist, then this new video will have the same PlaylistItem.id.
Any recommendations how to fake a real unique ID?
I think that the tuple
<playlistId, playlistItemId, videoId>
could be taken as a globally unique playlist item ID. Of course, for t1 := <p1, i1, v1> and t2 := <p2, i2, v2>, by definition t1 == t2 if and only if:
p1 == p2, and
i1 == i2, and
v1 == v2.
Since each component of such a tuple is a string that contains no comma, the tuple itself can simply be represented by the concatenation of these three strings separated by comma.
Encoding the ID tuples as mentioned implies that the componentwise ID tuples equality (as defined above) becomes trivially the string equality.
Decoding such an ID to its components is also trivial. Any modern language has readily available standard functions to do precisely such operation. For example, in Python that function is str.split; in PHP that is explode.
Related
I have a table of strings like this:
{
"1",
"1.5",
"3.13",
"1.2.5.7",
"2.5",
"1.3.5",
"2.2.5.7.10",
"1.17",
"1.10.5",
"2.3.14.9",
"3.5.21.9.3",
"4"
}
And would like to sort that like this:
{
"1",
"1.2.5.7",
"1.3.5",
"1.5",
"1.10.5",
"1.17",
"2.2.5.7.10",
"2.3.14.9",
"2.5",
"3.5.21.9.3",
"3.13",
"4"
}
How do I sort this in Lua? I know that table.sort() will be used, I just don't know the function (second parameter) to use for comparison.
Given your requirements, you probably want something like natural sort order. I described several possible solution as well as their impact on the results in a blog post.
The simplest solution may look like this (below), but there are 5 different solutions listed with different complexity and the results:
function alphanumsort(o)
local function padnum(d) return ("%03d%s"):format(#d, d) end
table.sort(o, function(a,b)
return tostring(a):gsub("%d+",padnum) < tostring(b):gsub("%d+",padnum) end)
return o
end
table.sort sorts ascending by default. You don't have to provide a second parameter then. As you're sorting strings Lua will compare the strings character by character. Hence you must implement a sorting function that tells Lua which comes first.
I just don't know the function (second parameter) to use for
comparison.
That's why people wrote the Lua Reference Manual
table.sort (list [, comp])
Sorts the list elements in a given order, in-place, from list1 to
list[#list]. If comp is given, then it must be a function that
receives two list elements and returns true when the first element
must come before the second in the final order, so that, after the
sort, i <= j implies not comp(list[j],list[i]). If comp is not given,
then the standard Lua operator < is used instead.
The comp function must define a consistent order; more formally, the
function must define a strict weak order. (A weak order is similar to
a total order, but it can equate different elements for comparison
purposes.)
The sort algorithm is not stable: Different elements considered equal
by the given order may have their relative positions changed by the
sort.
Think about how you would do it with pen an paper. You would compare each number segment. As soon as a segment is smaller than the other you know this number comes first.
So a solution would probably require you to get those segments for the strings, convert them to numbers so you can compare their values...
I have a topic called customers and I have created a stream for it
CREATE STREAM customers_stream (customerId INT, isActive BOOLEAN)
WITH (KAFKA_TOPIC='customers', VALUE_FORMAT='json');
My producer for customers topic is generating a Integer key and a json value. But when I see the row key is being set to a some binary value
ksql> print 'customers';
Format:JSON
{"ROWTIME":1570305904984,"ROWKEY":"\u0000\u0000\u0003�","customerId":1001,"isActive":true}
{"ROWTIME":1570307584257,"ROWKEY":"\u0000\u0000\u0003�","customerId":1002,"isActive":true}
Now if i create a table it results in a single row (maybe because row key is the same??)
CREATE TABLE customers (customerId INT, isActive BOOLEAN)
WITH (KAFKA_TOPIC='customers', KEY='customerId',VALUE_FORMAT='json');
After searching the web I bumped into this article https://www.confluent.io/stream-processing-cookbook/ksql-recipes/setting-kafka-message-key and created a new stream by repartitioning on the key
CREATE STREAM customers_stream2 AS \
SELECT * FROM customers_stream \
PARTITION BY customerId;
So how do I create a table which has the latest values of customers data?
creating a table from stream is resulting in a error
CREATE TABLE customers_2_table_active AS
SELECT CUSTOMERID,ISACTIVE
FROM customers_stream2;
Invalid result type. Your SELECT query produces a STREAM. Please use CREATE STREAM AS SELECT statement instead.
I need the latest value of the various rows so that another microservice can query the new table.
Thank you in advance
Rekeying seems to be the right approach, however, you cannot convert a STREAM into a TABLE directly.
Note, that your rekeyed stream customers_stream2 is written into a corresponding topic. Hence, you should be able to crate a new TABLE from the stream's topic to get the latest value per key.
Recently, I am experimenting Neo4j. I like the idea but I am facing a problem that I have never faced with relational databases.
I want to perform these inserts and then return them exactly in the insertion order.
Insert elements:
create(p1:Person {name:"Marc"})
create(p2:Person {name:"John"})
create(p3:Person {name:"Paul"})
create(p4:Person {name:"Steve"})
create(p5:Person {name:"Andrew"})
create(p6:Person {name:"Alice"})
create(p7:Person {name:"Bob"})
While to return them:
match(p:Person) return p order by id(p)
I receive the elements in the following order:
Paul
Andrew
Marc
John
Steve
Alice
Bob
I note that these elements are not returned respecting the query insertion order (through the id function).
In fact the id of my elements are the following:
Marc: 18221
John: 18222
Paul: 18208
Steve: 18223
Andrew: 18209
Alice: 18224
Bob: 18225
How does the Neo4j id function work? I read that it generates an auto incremental id but it seems a little strange his mechanism. How do I return items respecting the query insertion order? I thought about creating a timestamp attribute for each node but I don't think it's the best choice
If you're looking to generate sequence numbers in Neo4j then you need to manage this yourself using a strategy that works best in your application.
In ours we maintain sequence numbers in key/value pair nodes where Scope is the application name given to the sequence number range, and Value is the last sequence number used. When we generate a node of a given type, such as Product, then we increment the sequence number and assign it to our new node.
MERGE (n:Sequence {Scope: 'Product'})
SET n.Value = COALESCE(n.Value, 0) + 1
WITH n.Value AS seq
CREATE (product:Product)
SET product.UniqueId = seq
With this you can create as many sequence numbers you need just by creating sequence nodes with unique scope names.
For more examples and tests see the AutoInc.Neo4j project https://github.com/neildobson-au/AutoInc/blob/master/src/AutoInc.Neo4j/Neo4jUniqueIdGenerator.cs
The id of Neo4j is maintained internally, which your business code should not depend on.
Generally it's auto incrementally, but if there is delete operation, you may reuse the deleted id according to the Reuse Policy of Neo4j Server.
I got a few - company, location and product details to store in a db.
sample data
company location product
------------------------------
abc hilltop alpha
abc hilltop beta
abc riverside alpha
abc riverside beta
buggy underbridge gama
buggy underbridge theta
buggy underbridge omega
The relationships are multi-valued, as I understand. And the data needs to be normalized as the MVD's are
not derived from a candidate key (company ->> location and company ->> product where company is not a candidate key)
or the union does not make the whole set (company U location < R and so with product).
But my colleague disagrees with me, who insists that for a relation to have multi-valued dependency at least four same values in company column should exist for each company. i.e
t1(company) = t2(company) = t3(company) = t4(company),
for company abc this is true. But for company "buggy", which does only one product in three locations, this is untrue.
For the formal definition and similar examples I refernced:
https://en.wikipedia.org/wiki/Multivalued_dependency
and Fourth_normal_form example also on wiki.
I know my colleague is being pedagogy, but I too started seeing the same question after reading the formal definition. (After all these are derived on mathematical basis.)
update: I am not asking how to normalize this data in to 4NF, I think I know that. (I need to break it in to two tables 1) company - location and 2) company - product.
which I have done already.
Can some one explain how this relation is still a MVD even though it does not satisfy the formal definition?
Detailed explanations are very much welcome.
"There exist" says some values exist, and they don't have to be different. EXISTS followed by some name(s) says that there exist(s) some value(s) referred to by the name(s), for which a condition holds. Multiple names can refer to the same value. (FOR ALL can be expressed in terms of EXISTS.)
The notion of MVD can be applied to both variables and values. In fact the form of the linked definition is that a MVD holds in the variable sense when it holds in the value sense "in any legal relation". To know that a particular value is legal, you need business knowledge. You can then show whether that value satisfies an MVD. But to show whether its variable satisfies the MVD you have to show that the MVD is satisfied "in any legal relation" value that the variable can hold. One valid value can tell you that a MVD doesn't hold in (it and) its variable, but it can't tell you that a MVD does hold in its variable. That requires more business knowledge.
You can show that this value violates 4NF by using that definition of MVD. The definition says that a relation variable satisfies a MVD when a certain condition holds "for any valid relation" value:
for all pairs of tuples t1 & t2 in r such that t1[a] = t2[a] there exist tuples t3 & t4 [...]
For what MVD and values for t1 & t2 does your colleague claim there doesn't exist values for t3 & t4? There is no such combination of MVD and values for t1 & t2. Eg for {company} ↠ {product} and t1 & t2 both (buggy, underbridge, gamma), we can take (company, underbridge, gamma) as a value for both t3 & t4, and so on for all other choices for t1 & t2.
Another definition for F ↠ T holding is that binary JD (join dependency) *{F U T, F U (A - T)} holds, ie that the relation is equal to the join of its projections on F U T & F U (A - T). This definition might be more immediately helpful to you & your colleague in that it avoids the terminology that you & they are misinterpreting. Eg your example data is the join of these two of its projections:
company location
--------------------
abc hilltop
abc riverside
buggy underbridge
company product
----------------
abc alpha
abc beta
buggy gamma
buggy theta
buggy omega
So it satisfies the JD *{{company, location}, {company, product}}, so it satisfies the MVDs {company} ↠ {location} and {company} ↠ {product} (among others). (Maybe you will be able to think of examples of relations with zero, one, two, three etc tuples for which one or more (trivial and/or non-trivial) MVDs hold.)
Of course, the two definitions are two different ways of describing the same condition.
PS 1 Whenever a FD F → T holds, the MVD F ↠ T holds. For a relation in BCNF, the MVDs that violate 4NF & 5NF are those not so associated with FDs.
PS 2 A relation variable is meant to hold a tuple if and only if it makes a true statement in business terms when its values are substituted into a given statement template, or predicate. That plus the JD definition for MVD gives conditions for a relation variable satisfying a MVD in business terms. Here our predicate is of the form ...company...location...product.... (Eg company namedcompanyis located atlocationand makes productproduct.) It happens that this MVD holds for a variable when for all valid business situations, FOR ALL company, location, product,
EXISTS product [...company...location...product...]
AND EXISTS location [...company...location...product...]
IMPLIES ...company...location...product...
I am trying to use PlaylistItems: list (method) in my java code.
The code itself is irrelevant here as the problem can be replicated with use of Youtube API examples here
https://developers.google.com/youtube/v3/docs/playlistItems/list
The problem:
While video with specific id exists in the playList,
when using list query on playlistlist filtered by video id and maxResults < of the vieo's sequence number, the result returned is an empty list instead of list with that specific video.
For example:
https://developers.google.com/youtube/v3/docs/playlistItems/list
part = snippet,id
playlistId = PL6894BC5B5D452193
videoId = xEsC1tw-pOw
maxResults = 5 (default value)
(the 11th video in litst)
Result is empty list.
But if i search for
part = snippet,id
playlistId = PL6894BC5B5D452193
videoId = m1V1SjMD1lo
video is found
(the 1st video in list)
As far as I can tell the reason is the value of
maxResults parameter.
However in a real world scenario - my list contains more that 100 items and the max allowed value for maxResults is 50.
So is there a way to find the correct video using list method?
Is this a bug or am I missing something?