Python - get max temp based on city-CodePudding

I'm quite new to Python and struggling to get my head round the logic in this for loop. My data has two values, a city and a temp. I would like to write a "for loop" that outputs the maximum temp for each city as follows:

PAR 31
LON 23
RIO 36
DUB 44

As it is to be used in Hadoop, I can't use any python libraries.

Here is my dataset:

['PAR,31',
 'PAR,18',
 'PAR,14',
 'PAR,18',
 'LON,12',
 'LON,13',
 'LON,9',
 'LON,23',
 'LON,5',
 'RIO,36',
 'RIO,33',
 'RIO,21',
 'RIO,25',
 'DUB,44',
 'DUB,42',
 'DUB,38',
 'DUB,34']

This is my code:

current_city = None
current_max = 0

for line in lines:
    (city, temp) = line.split(',')
   
    temp = int(temp)
    
    if city == current_city:
        if current_max < temp:
            current_max == temp

    current_city = city
            
print(current_city, current_max)

This was my output:

DUB 0

CodePudding user response：

You could iterate over your list. Separate your data. Check if the City is already in the dictionary. If so check if the temp is higher as the one saved in the dictionary if that's the case replace the entry in the dictionary.

If the city isn't in the dictionary simply add it into the dictionary.


a = ['PAR,31',
 'PAR,18',
 'PAR,14',
 'PAR,18',
 'LON,12',
 'LON,13',
 'LON,9',
 'LON,23',
 'LON,5',
 'RIO,36',
 'RIO,33',
 'RIO,21',
 'RIO,25',
 'DUB,44',
 'DUB,42',
 'DUB,38',
 'DUB,34']

dict = {}
for entry in a:
    city,temp = entry.split(",")
    if city in dict.keys():
        if dict[city] < int(temp):
            dict[city] = int(temp)
    else:
        dict[city] = int(temp)

print(dict)

Output:

{'PAR': 31, 'LON': 23, 'RIO': 36, 'DUB': 44}

CodePudding user response：

Build a dictionary keyed on city names. The associated values should be a list of integers (the temperatures).

Once the dictionary has been constructed you can then iterate over its items to determine the highest value in each list of temperatures,

data = ['PAR,31',
        'PAR,18',
        'PAR,14',
        'PAR,18',
        'LON,12',
        'LON,13',
        'LON,9',
        'LON,23',
        'LON,5',
        'RIO,36',
        'RIO,33',
        'RIO,21',
        'RIO,25',
        'DUB,44',
        'DUB,42',
        'DUB,38',
        'DUB,34']
d = {}
for city, temp in map(lambda e: e.split(','), data):
    d.setdefault(city, []).append(int(temp))
for k, v in d.items():
    print(k, max(v))

Output:

PAR 31
LON 23
RIO 36
DUB 44

CodePudding user response：

Given the answers here are a bit verbose…

result = {}

for l in lines:
    city, t = l.split(',')
    t = int(t)
    result[city] = max(result.setdefault(city, t), t)

# you can print result however you like, e.g.:
for c, t in result.items():
    print(f"{c} {t}")