aggregation

问题 sample of my document { _id: "bmasndvhjbcw", name: "lucas", occupation: "scientist", present_working:true, age: 55, location: "texas", }, { _id: "bmasndvhjbcx", name: "mark", occupation: "scientist", age: 45, present_working:true, location: "texas", }, { _id: "bmasndvhjbca", name: "stuart", occupation: "lab assistant", age: 25, location: "texas", }, { _id: "bmasndvhjbcq", name: "cooper", occupation: "physicist", age: 69, location: "texas" } ] For the records which doesn't have present_working

问题 I am using MySQL server via Amazon could service, with default settings. The table involved mytable is of InnoDB type and has about 1 billion rows. The query is: select count(*), avg(`01`) from mytable where `date` = "2017-11-01"; Which takes almost 10 min to execute. I have an index on date . The EXPLAIN of this query is: +----+-------------+---------------+------+---------------+------+---------+-------+---------+-------+ | id | select_type | table | type | possible_keys | key | key_len |

问题 so I have a collection users , and each document in this collection, as well as other properties, has an array of ids of documents in the other collection: workouts . Every document in the collection workouts has a property named date . And here's what I want to get: For a specific user, I want to get an array of {workoutId, workoutDate} for the workouts that belong to that user, sorted by date. This is my attempt, which is working fine. Users.aggregate([ { $match : { _id : ObjectId(

问题 Hello I have this question: I would like to have a vector as class member. This is perhaps my question easier for you and I apologize for that. how should I declare the vector? And is this correct? std::vector<int> *myVector; or std::vector<int> myVector ? how should I handle this vector in dealloc? How can I initialize the array into a if? Is this correct? if(myCondition) { if(!myVector) //is this correct? myVector = new std::vector<int>(); //is this correct? on this i have a error } 回答1:

问题 I want to find out how many times a particular value occured consecutively for a particular partition and then display the higher count for that partition. For Example if below is the table: Device ID speed DateTime -------------------------------------------------- 07777778999 34 18-12-2016 17:15 07777778123 15 18-12-2016 18:10 07777778999 34 19-12-2016 19:30 07777778999 34 19-12-2016 12:15 07777778999 20 19-12-2016 13:15 07777778999 20 20-12-2016 11:15 07777778123 15 20-12-2016 9:15

问题 I have a Pandas data frame like this: test = pd.DataFrame({ 'Date' : ['2016-04-01','2016-04-01','2016-04-02', '2016-04-02','2016-04-03','2016-04-04', '2016-04-05','2016-04-06','2016-04-06'], 'User' : ['Mike','John','Mike','John','Mike','Mike', 'Mike','Mike','John'], 'Value' : [1,2,1,3,4.5,1,2,3,6] }) As you can see below, the data set does not have observations for every day necessarily: Date User Value 0 2016-04-01 Mike 1.0 1 2016-04-01 John 2.0 2 2016-04-02 Mike 1.0 3 2016-04-02 John 3.0 4

问题 I have a Pandas data frame like this: test = pd.DataFrame({ 'Date' : ['2016-04-01','2016-04-01','2016-04-02', '2016-04-02','2016-04-03','2016-04-04', '2016-04-05','2016-04-06','2016-04-06'], 'User' : ['Mike','John','Mike','John','Mike','Mike', 'Mike','Mike','John'], 'Value' : [1,2,1,3,4.5,1,2,3,6] }) As you can see below, the data set does not have observations for every day necessarily: Date User Value 0 2016-04-01 Mike 1.0 1 2016-04-01 John 2.0 2 2016-04-02 Mike 1.0 3 2016-04-02 John 3.0 4

问题 Consider the following (abstract) situation: Two entities. There are two aggregation relationships between the two entities. The diagram looks like this: I know this might sound vague, but is there anything wrong with this picture? I mean, are there any (obvious) problems that could arise from this kind of design? Or am I being paranoid and there's absolutely nothing wrong with two (or more) aggregation relationships between two entities? 回答1: For me there is nothing wrong in such design.

问题 df: hour rev datetime 2016-05-01 01:00:00 1 -0.02 2016-05-01 02:00:00 2 -0.01 2016-05-01 03:00:00 3 -0.02 2016-05-01 04:00:00 4 -0.02 2016-05-01 05:00:00 5 -0.01 2016-05-01 06:00:00 6 -0.03 2016-05-01 07:00:00 7 -0.10 2016-05-01 08:00:00 8 -0.09 2016-05-01 09:00:00 9 -0.08 2016-05-01 10:00:00 10 -0.10 2016-05-01 11:00:00 11 -0.12 2016-05-01 12:00:00 12 -0.14 2016-05-01 13:00:00 13 -0.17 2016-05-01 14:00:00 14 -0.16 2016-05-01 15:00:00 15 -0.15 2016-05-01 16:00:00 16 -0.15 2016-05-01 17:00:00

问题 There are two collections: Sales { "_id" : ObjectId("5ba0bfb8d1acdc0de716e839"), "invoiceNumber" : 1, "saleDate" : ISODate("2018-09-01T00:00:00.000Z"), "totalTaxAmount" : 613, "subTotalAmount" : 2000, "totalAmount" : 2613, "balance" : 2613, "financialYear" : "2018-2019", "modeOfPayment" : "Digital Transfer", "customerName": "Acme Inc" } Transactions { "_id" : ObjectId("5bbb4e131fb8af0dc645212d"), "transactionNumber" : 1 "transactionDate" : ISODate("2018-09-03T00:00:00.000Z"), "transactionType