- Trending Categories
Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
How to perform cartesian join for two data.table objects in R?
The cartesian join is the joining of two objects that creates the combination of each value in object with all the values in the other object. For example, if we have a vector x that contains 1, 2, 3 and the other object y contains a, b, c then the cartesian join will be 1a, 2a, 3a, 1b, 2b, 3b, 1c, 2c, and 3c. Check out the below examples to understand how it can be done.
Example
> library(data.table) > DT1<-data.table(x=1:4) > DT1
Output
x 1: 1 2: 2 3: 3 4: 4
Example
> DT2<-data.table(y=25:30) > DT2
Output
y 1: 25 2: 26 3: 27 4: 28 5: 29 6: 30
Performing cartesian join of DT1 and DT2:
Example
> DT1[,as.list(DT2),by=DT1]
Output
x y 1: 1 25 2: 1 26 3: 1 27 4: 1 28 5: 1 29 6: 1 30 7: 2 25 8: 2 26 9: 2 27 10: 2 28 11: 2 29 12: 2 30 13: 3 25 14: 3 26 15: 3 27 16: 3 28 17: 3 29 18: 3 30 19: 4 25 20: 4 26 21: 4 27 22: 4 28 23: 4 29 24: 4 30 x y
Let’s have a look at another example:
Example
> DT_G<-data.table(Group=LETTERS[1:5]) > DT_G
Output
Group 1: A 2: B 3: C 4: D 5: E
Example
> DT_Count<-data.table(sample(21:50,5)) > DT_Count
Output
V1 1: 22 2: 28 3: 45 4: 31 5: 47
Performing cartesian join of DT_G and DT_Count:
Example
> DT_G[,as.list(DT_Count),by=DT_G]
Output
Group V1 1: A 22 2: A 28 3: A 45 4: A 31 5: A 47 6: B 22 7: B 28 8: B 45 9: B 31 10: B 47 11: C 22 12: C 28 13: C 45 14: C 31 15: C 47 16: D 22 17: D 28 18: D 45 19: D 31 20: D 47 21: E 22 22: E 28 23: E 45 24: E 31 25: E 47 Group V1
Advertisements