python - Creating Max and Min list for Rolling Sublists

Question

I have a list that contains sublists:

[{'h': '20', 'l': '9'}, {'h': '30', 'l': '20'}, {'h': '25', 'l': '7'}, {'h': '18', 'l': '19'}, {'h': '22', 'l': '3'}]

I wish to work my way from left to right, finding the max for 'h' and the min for 'l' within the decreasing number of remaining sublists, including the current sublist being referenced. The result should be as follows.

[{'h': '30', 'l': '3'}, {'h': '30', 'l': '3'}, {'h': '25', 'l': '3'}, {'h': '22', 'l': '3'}, {'h': '22', 'l': '3'}]

Finding the max and min of the whole list is easy enough, but I cannot figure out the best way to "discard" the preceding subsists and only use the remaining sublists in creating the new list.

question from:https://stackoverflow.com/questions/65923001/creating-max-and-min-list-for-rolling-sublists

Answer 1

This code solves your question:

inp = [{'h': '20', 'l': '9'}, {'h': '30', 'l': '20'}, {'h': '25', 'l': '7'}, {'h': '18', 'l': '19'}, {'h': '22', 'l': '3'}]
l1 = inp[::-1]
l2 = []

max1 = int(l1[0]['h'])
min1 = int(l1[0]['l'])
for item in l1:
  max1 = int(item['h']) if int(item['h'])>max1 else max1
  min1 = int(item['l']) if int(item['l'])<min1 else min1
  l2.append({'h':str(max1),'l':str(min1)})

l2 = l2[::-1]
print(l2)

Output

[{'h': '30', 'l': '3'}, {'h': '30', 'l': '3'}, {'h': '25', 'l': '3'}, {'h': '22', 'l': '3'}, {'h': '22', 'l': '3'}]

More info

First, I reversed the input list and named it l1 then I iterate over l1 holding the current max1 for h and min1 for l. I appended the max1 and min1 to l2 in each iteration. and finally I reversed the l2 list.