group-by

问题 I have some arrays like this: array( 'id' => 1, 'title' => 'title1', 'name' => 'name1', 'count' => 2 ) array( 'id' => 1, 'title' => 'title1', 'name' => 'name2', 'count' => 3 ) array( 'id' => 2, 'title' => 'title2', 'name' => 'name1', 'count' => 2 ) I want to merge them so that arrays with same id and title would be merged. The result should be like: array( 'id' => 1, 'title' => 'title1', 'name' => array('name1', 'name2'), 'count' => array(2, 3) ) array( 'id' => 2, 'title' => 'title2', 'name'

问题 lets say I have following data ind1 <- rnorm(99) ind2 <- rnorm(99) ind3 <- rnorm(99) ind4 <- rnorm(99) ind5 <- rnorm(99) dep <- rnorm(99, mean=ind1) group <- rep(c("A", "B", "C"), each=33) df <- data.frame(dep,group, ind1, ind2, ind3, ind4, ind5) the following code is calculating multiple linear regression between dependend variable and 2 independent variables by group which is exactly what I want to do. But I want to regress dep variable against all combination pair of independent variables

问题 I have a pandas dataframe with multiindex where I want to aggregate the duplicate key rows as follows: import numpy as np import pandas as pd df = pd.DataFrame({'S':[0,5,0,5,0,3,5,0],'Q':[6,4,10,6,2,5,17,4],'A': ['A1','A1','A1','A1','A2','A2','A2','A2'], 'B':['B1','B1','B2','B2','B1','B1','B1','B2']}) df.set_index(['A','B']) Q S A B A1 B1 6 0 B1 4 5 B2 10 0 B2 6 5 A2 B1 2 0 B1 5 3 B1 17 5 B2 4 0 and I would like to groupby this dataframe to aggregate the Q values (sum) and keep the S value

问题 I have a dataframe that currently looks somewhat like this. import pandas as pd In [161]: pd.DataFrame(np.c_[s,t],columns = ["M1","M2","M1","M2"]) Out[161]: M1 M2 M1 M2 6/7 1 2 3 5 6/8 2 4 7 8 6/9 3 6 9 9 6/10 4 8 8 10 6/11 5 10 20 40 Except, instead of just four columns, there are approximately 1000 columns, from M1 till ~M340 (there are multiple columns with the same headers). I wanted to sum the values associated with matching columns based on their index. Ideally, the result dataframe

问题 I have read much in textbooks and browsed a lot of pages on the internet but I can't understand how functions/operators like min, max, count, ... that aggregate over a relation/table or groups of tuples/rows in a relation/table are built with basic operations such as ∪ (union), ∩ (intersection), x (join), - (minus), π (projection), .... Can anyone show me how to express these functions/operators with relational algebra? 回答1: Computing functions in relation algebra are not fully included yet.

问题 I have read much in textbooks and browsed a lot of pages on the internet but I can't understand how functions/operators like min, max, count, ... that aggregate over a relation/table or groups of tuples/rows in a relation/table are built with basic operations such as ∪ (union), ∩ (intersection), x (join), - (minus), π (projection), .... Can anyone show me how to express these functions/operators with relational algebra? 回答1: Computing functions in relation algebra are not fully included yet.

问题 I’ve searched and I know this has been asked before but I am struggling to get my head around what I can / can’t do. My cycling club records race results each time a rider has entered a race. Each result is awarded points - 50 for 1st, 49 for 2nd etc. So the table looks like resultid(pk) | riderid(fk) | leaguepts 1 1 50 2 2 49 3 3 48 4 1 50 5 2 42 6 3 50 7 4 30 ...etc I am trying to extract the sum of top 10 points awarded for each riderid from the results table. (the actual database is a bit

问题 I have a pandas dataframe that looks as follows: ID round player1 player2 1 1 A B 1 2 A C 1 3 B D 2 1 B C 2 2 C D 2 3 C E 3 1 B C 3 2 C D 3 3 C A The dataframe contains sport match results, where the ID column denotes one tournament, the round column denotes the round for each tournament, and player1 and player2 columns contain the names of players that played against eachother in the respective round . I now want to cumulatively count the tournament participations for, say, player A . In

问题 I have a problem in Oracle SQL that I'm trying to get my head around. I'll illustrate with an example. I have three tables that I am querying: Employees __________________________________________ | EmployeeID | Name | | 1 | John Smith | | 2 | Douglas Hoppalot | | 3 | Harry Holiday | ... InternalCosts ________________________________ | IntID | Amount | EmployeeID | | 1 | 10 | 1 | | 2 | 20 | 2 | | 3 | 30 | 1 | ... ExternalCosts ________________________________ | ExtID | Amount | EmployeeID | |

问题 I have a problem in Oracle SQL that I'm trying to get my head around. I'll illustrate with an example. I have three tables that I am querying: Employees __________________________________________ | EmployeeID | Name | | 1 | John Smith | | 2 | Douglas Hoppalot | | 3 | Harry Holiday | ... InternalCosts ________________________________ | IntID | Amount | EmployeeID | | 1 | 10 | 1 | | 2 | 20 | 2 | | 3 | 30 | 1 | ... ExternalCosts ________________________________ | ExtID | Amount | EmployeeID | |