join

问题 Say I have two large RDD's, A and B, containing key-value pairs. I want to join A and B using the key, but of the pairs (a,b) that match, I only want a tiny fraction of "good" ones. So I do the join and apply a filter afterwards: A.join(B).filter(isGoodPair) where isGoodPair is a boolean function that tells me if a pair (a,b) is good or not. For this to scale well, Spark's scheduler would ideally avoid forming all pairs in A.join(B) explicitly. Even on a massively distributed basis, this

问题 I need to know if is it possible to join two or more contacts (in a programmatic way, using the Contacts android API or something). For example, I have a contact "Axel Rose" with an email account and a phone number, and I've noticed that some apps like whatsapp, Facebook and Skype are creating new contact entries for Axel Rose, instead of merging the existing one. I can join contacts using the "Join feature" from the phone, but is there a programmatic way? Thanks in advance. Cristian. 回答1:

问题 I have two data frames. The first one has two columns: x is water depth, y is temperature at each depth. The second one has two columns too, x is also water depth, but at different depth compared to that in the first table. The second column z is salinity. I want to join the two tables by x , by adding z to the first table. I have learned how to join tables using 'key' in tidyr , but that only works if the keys are identical. The x in these two tables are not the same. What I want to do is to

问题 I have two data frames. The first one has two columns: x is water depth, y is temperature at each depth. The second one has two columns too, x is also water depth, but at different depth compared to that in the first table. The second column z is salinity. I want to join the two tables by x , by adding z to the first table. I have learned how to join tables using 'key' in tidyr , but that only works if the keys are identical. The x in these two tables are not the same. What I want to do is to

问题 I have a query like this: select a1.name, b1.info from (select name, id, status from table1 a) as a1 right outer join (select id, info from table2 b) as b1 on (a1.id = b1.id) I only want to include everything where a1.status=1 and since I'm using an outer join, I can't just add a where constraint to table1, because all info from table2 that I want to be excluded will still be there, just without the name. I was thinking something like this: select z1.name, z1.info from ((select name, id,

问题 I have 3dataframes generated from 3 different processes. Every dataframe is having columns of same name. My dataframe looks like this id val1 val2 val3 val4 1 null null null null 2 A2 A21 A31 A41 id val1 val2 val3 val4 1 B1 B21 B31 B41 2 null null null null id val1 val2 val3 val4 1 C1 C2 C3 C4 2 C11 C12 C13 C14 Out of these 3 dataframes, i want to create two dataframes, (final and consolidated). For final, order of preferences - dataFrame 1 > Dataframe 2 > Dataframe 3 If a result is there in

问题 I have 3dataframes generated from 3 different processes. Every dataframe is having columns of same name. My dataframe looks like this id val1 val2 val3 val4 1 null null null null 2 A2 A21 A31 A41 id val1 val2 val3 val4 1 B1 B21 B31 B41 2 null null null null id val1 val2 val3 val4 1 C1 C2 C3 C4 2 C11 C12 C13 C14 Out of these 3 dataframes, i want to create two dataframes, (final and consolidated). For final, order of preferences - dataFrame 1 > Dataframe 2 > Dataframe 3 If a result is there in

问题 I read that in nosql (cassandra for instance) data is often stored denormalized. For instance see this SO answer or this website. An example is if you have a column family of employees and departments and you want to execute a query: select * from Emps where Birthdate = '25/04/1975' Then you have to make a column family birthday_Emps and store the ID of each employee as a column. So then you can query the birthday_Emps family for the key '25/04/1975' and instantly get all the ID's of the

问题 I have two tables with similar column names and I need to return records from the left table which are not found in the right table? I have a primary key(column) which will help me to compare both tables. Which join is preferred? 回答1: If you are asking for T-SQL then lets look at fundamentals first. There are three types of joins here each with its own set of logical processing phases as: A cross join is simplest of all. It implements only one logical query processing phase, a Cartesian

问题 It is for a system that calculates how the users scan their fingerprints when they enter/leave the workplace. I don't know how it is called in English. I need to determine if the user is late in the morning, and if the user leaves work early. This tb_scan table contains date and time a user scans a fingerprint. CREATE TABLE `tb_scan` ( `scpercode` varchar(6) DEFAULT NULL, `scyear` varchar(4) DEFAULT NULL, `scmonth` varchar(2) DEFAULT NULL, `scday` varchar(2) DEFAULT NULL, `scscantime`