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Associatively sorting a table by value in Lua
(7 answers)
Closed 9 years ago.
I need help on this table
tbl = {
Noa={10,0,3},
melvin={5,3,1},
jeex={500,0,2},
kiim={100,2,3}
}
I neet all valueson this table, sort by first value on table
example.
output>
jeex 500 ,0,2
kiim 100 ,2,3
Noa 10,0,3
melvin 5,3,1
Only table elements with numerical indices have an order. You can't sort a table where the keys are strings. So your first step is to create a table that actually has an order. You do this by iterating through the elements of your current table and insert a value in a new table based on the current one, one that contains both the key and the value.
local array = {}
for key, value in pairs(tbl) do
array[#array + 1] = {key = key, value = value}
end
Once you have an actual array, then you can sort it with table.sort.
Related
I'm trying to query a dynamodb table using the partition key and a sort key. The sort key is a unix date, so I want to request x partition key between these 2 dates on the sort. I am currently able to achieve this with a table scan, but I have to move this to a query for the speed benefit. I am unable to find any decent examples online of people using a partition key and sort key to query their table.
I have carefully read through this https://docs.aws.amazon.com/sdk-for-go/api/service/dynamodb/#DynamoDB.Query and understand that my params must go within the KeyConditionExpression.
I have read through https://github.com/aws/aws-sdk-go/blob/master/service/dynamodb/expression/examples_test.go and understand it on the whole. But I just can't find the syntax for KeyConditionExpression
I'd have thought it was something like this:
keyCond := expression.Key("accountId").
Equal(expression.Value(accountId)).
And(expression.Key("sortKey").
Between(expression.Value(fromDateDec), expression.Value(toDateDec)))
But this throws:
ValidationException: Invalid KeyConditionExpression: Incorrect operand type for operator or function; operator or function: BETWEEN, operand type: NULL
First you need KeyAnd to combine Hash Key and sort key condition.
// keyCondition represents the key condition where the partition key
// "TeamName" is equal to value "Wildcats" and sort key "Number" is equal
// to value 1
keyCondition := expression.KeyAnd(expression.Key("TeamName").Equal(expression.Value("Wildcats")), expression.Key("Number").Equal(expression.Value(1)))
Now instead equal condition you can replace with your between condition as follows
// keyCondition represents the boolean key condition of whether the value
// of the key "foo" is between values 5 and 10
keyCondition := expression.KeyBetween(expression.Key("foo"), expression.Value(5), expression.Value(10))
I'm a bit new to LUA. So I have a game that I need to capture the Entity and insert into the table. The maximum possible Entity table that could happen at the same time is 14. So I read that an array based solution is good.
But I saw that the table size increment even if we delete some value, for example from 10 table value and delete value at index 9 its not automatically shift the size when I want to insert table number 11.
Example:
local Table = {"hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello"}
-- Current Table size = 10
-- Perform delete at index 9
Table[9] = nil
-- Have new Entity to insert
Table[#Table + 1] = "New Value"
-- The table size will grow by the time the game extend.
So for this type of situation did array based table with nil value inside that grow by the time of new table value inserted will have better perfomance or should I move into table with key?
Or I should just stick with array based table and perform full cleanup when the table isnt used?
If you set an element in a table to nil, then that just stays there as a "hole" in your array.
tab = {1, 2, 3, 4}
tab[2] = nil
-- tab == {1, nil, 3, 4}
-- #tab is actually undefined and could be both 1 or 4 (or something completely unexpected)!
What you need to do is set the field to nil, then shift all the following fields to fill that hole. Luckily, Lua has a function for that, which is table.remove(table, index).
tab = {1, 2, 3, 4}
table.remove(tab, 2)
-- tab == {1, 3, 4}
-- #tab == 3
Keep in mind that this can get very slow as there's lots of memory access involved, so don't go applying this solution when you have a few million elements some day :)
While table.remove(Table, 9) will do the job in your case (removing field from "array" table and shifting remaining fields to fill the hole), you should first consider using "set" table instead.
If you:
- often remove/add elements
- don't care about their order
- often check if table contains a certain element
then the "set" table is your choice. Use it like so
local tab = {
["John"] = true,
["Jane"] = true,
["Bob"] = true,
}
Your elements will be stored as indices in a table.
Remove an element with
tab["Jane"] = nil
Test if table contains an element with
if tab["John"] then
-- tab contains "John"
Advantages compared to array table:
- this will eliminate performance overhead when removing an element because other elements will remain intact and no shifting is required
- checking if element exists in this table (which I assume is the main puspose of this table) is also faster than using array table because it no longer requires iterating over all the elements to find a match, the hash lookup is used instead
Note however that this approach doesn't let you have duplicate values as your elements, because tables can't contain duplicate keys. In that case you can use numbers as values to store the amount of times the element is duplicated in your set, e.g.
local tab = {
["John"] = 1,
["Jane"] = 2,
["Bob"] = 35,
}
Now you have 1 John, 2 Janes and 35 Bobs
https://www.lua.org/pil/11.5.html
Lets say I have this code:
sql_query="select actor.actor_id from actor where actor='%s'"
cursor.execute=(sql_query,(actorID))
result=cursor.fetchall()
return(result)
What should I do to my code so the results are in the form of a list of tuples?Also I want the first tuple to be the name of the columns of my query.
For example: [(“Name”, “Id”,),(“Jim”,7,),(“Tom”,13,)]
Here is a sample example:
cur.execute('''SELECT * FROM patient_login''')
results = cur.fetchall()
nested_tuple_list = []
for result in results:
nested_tuple_list.append(result)
print(nested_tuple_list)
As you can see, we enter our select statement with cur.execute(). We fetch all of the results and store them in the variable results. We run a for loop, and each result will be a tuple of a result in our DB. We then append them to the end of the list. When we print the results, here is the output:
[(4, 'sikudabo', 'monkey1'), (83, 'sikudabo2', 'monkey2')]
We end up with a list of tuples.
Here is another answer that simple grabs the column names and stores them in a nested tuple:
cur.execute('''DESCRIBE patient_login''')
results = cur.fetchall()
nested_tuple_list = []
nested_tuple_list_2 = []
for result in results:
result = ((result[0]))
nested_tuple_list.append(result)
nested_tuple_list = tuple(nested_tuple_list)
nested_tuple_list_2.append(nested_tuple_list)
print(nested_tuple_list_2)
The describe command in SQL will Describe the table by telling you which columns exist within the table, and various characteristics of the table such as primary key, datatype ect. This command will return a tuple of the described data. Here we search each result and grab the first index in the results for each of the nested tuples. The first index corresponds with the column name in the for loop. We can append this to the first empty list. After we append all of the column names, we change the list to a tuple. We then append that tuple to the list and have all of the column names in the list within a tuple. Here is the output:
[('ID', 'username', 'password')]
If you want each element in the list to be a tuple in it of itself, here is the code:
nested_tuple_list = tuple(nested_tuple_list)
nested_tuple_list_2 = [(x,) for x in nested_tuple_list]
print(nested_tuple_list_2)
We can do a list comprehension with x representing each column, and here is our output for each of my columns in the DataFrame:
[('ID',), ('username',), ('password',)]
I have a clickhouse table that has one Array(UInt16) column. I want to be able to filter results from this table to only get rows where the values in the array column are above a threshold value. I've been trying to achieve this using some of the array functions (arrayFilter and arrayExists) but I'm not familiar enough with the SQL/Clickhouse query syntax to get this working.
I've created the table using:
CREATE TABLE IF NOT EXISTS ArrayTest (
date Date,
sessionSecond UInt16,
distance Array(UInt16)
) Engine = MergeTree(date, (date, sessionSecond), 8192);
Where the distance values will be distances from a certain point at a certain amount of seconds (sessionSecond) after the date. I've added some sample values so the table looks like the following:
Now I want to get all rows which contain distances greater than 7. I found the array operators documentation here and tried the arrayExists function but it's not working how I'd expect. From the documentation, it says that this function "Returns 1 if there is at least one element in 'arr' for which 'func' returns something other than 0. Otherwise, it returns 0". But when I run the query below I get three zeros returned where I should get a 0 and two ones:
SELECT arrayExists(
val -> val > 7,
arrayEnumerate(distance))
FROM ArrayTest;
Eventually I want to perform this select and then join it with the table contents to only return rows that have an exists = 1 but I need this first step to work before that. Am I using the arrayExists wrong? What I found more confusing is that when I change the comparison value to 2 I get all 1s back. Can this kind of filtering be achieved using the array functions?
Thanks
You can use arrayExists in the WHERE clause.
SELECT *
FROM ArrayTest
WHERE arrayExists(x -> x > 7, distance) = 1;
Another way is to use ARRAY JOIN, if you need to know which values is greater than 7:
SELECT d, distance, sessionSecond
FROM ArrayTest
ARRAY JOIN distance as d
WHERE d > 7
I think the reason why you get 3 zeros is that arrayEnumerate enumerates over the array indexes not array values, and since none of your rows have more than 7 elements arrayEnumerates results in 0 for all the rows.
To make this work,
SELECT arrayExists(
val -> distance[val] > 7,
arrayEnumerate(distance))
FROM ArrayTest;
I have an array of user info in #user_info and in array there is a column total and column user_id.
I have another instance variable #product and it has column user_id
How do i calculate sum of all values in column total verifying the user_id from #user_info and #product same?
I am trying to calcuate sum in controller, store it in instance variable and use that variable in JSON
Thanks
Try something like
#user_info.select { |user_info| user_info.user_id == #product.user_id }.sum(&:total)
or, if #user_info is not a simple Array, you should be able to do in one SQL query
#user_info.where(user_id: #product.user_id).sum(:total)