'''
20210930

Robin Dawes

Using lamda functions to sort things
'''

# a list of dimensions of some rectangles
list_a = [ [3, 7],
               [9, 5],
               [1, 8],
               [4, 12],
               [18, 2]   ]
               
               
               
print("Sorting rectangles by area")               
print ("Before sorting:",list_a)

list_a.sort(key = lambda x : x[0]*x[1])    #sort by the area of the rectangles
# the lambda function here is equivalent to
#       def <noname> (x):
#            return x[0]*x[1]

print("\nAfter sorting:", list_a)
               
print("\n\nSorting rectangles by largest dimension")

# using the built-in function "max" to determine the key for sorting
list_a.sort(key = lambda x : max(x))

print("\nAfter sorting:", list_a)

def avg(a, b):
   return (a+b)/2
   
print("\n\nSorting rectangles by average of dimensions")

# using a locally defined function to determine the key value
list_a.sort(key = lambda x : avg(x[0],x[1]))

print("\nAfter sorting:", list_a)