Set operations are super useful when data cleaning or testing scripts. They are a must have in any analyst’s (data scientist’s/statistician’s/data wizard’s) toolbox. Here is a quick rundown in both R and python.
Say we have two vectors x and y…
# vector x x = c(1,2,3,4,5,6) # vector y y = c(4,5,6,7,8,9)
What if we ‘combined’ x and y ignoring any duplicate elements? ()
# x UNION y union(x, y)  1 2 3 4 5 6 7 8 9
What are the common elements in x and y? ()
# x INTERSECTION y intersect(x, y)  4 5 6
What elements feature in x but not in y?
# x members not in y setdiff(x,y)  1 2 3
What elements feature in y but not in x?
# y members not in x setdiff(y,x)  7 8 9
How might we visualise all this?
What about python? In standard python there exists a module called ‘sets’ that allows for the creation of a ‘Set’ object from a python list. The Set object has methods that provide the same functionality as the R functions above.