Python sort() issue with negative values

Question

Good day everyone,

I ran into a problem when sorting percentage values in my dict with the sorted() function. When i get to the negative numbers it sorts the largest negative number first followed by the second largest etc. I want the smallest negative number to appear first. Is there any way to modify my sorted() to achieve this? Cheers!

yoy_dict = sorted(yoy_dict.items(), key=lambda x: x[1], reverse = True)

yoy_dict = [('HOUGANG', '1.130759%'),

 ('JURONG EAST', '0.786807%'),

 ('PUNGGOL', '0.238738%'),

 ('SEMBAWANG', '-2.150383%'),

 ('WOODLANDS', '-2.043103%'),

 ('CHOA CHU KANG', '-1.923021%'),

 ('SENGKANG', '-1.548278%'),

 ('MARINE PARADE', '-1.445532%'),

 ('CENTRAL AREA', '-1.266556%'),

 ('JURONG WEST', '-1.037612%'),

 ('YISHUN', '-0.843832%'),

 ('BUKIT BATOK', '-0.296952%')]

Answer 1

You need to convert your values to float to avoid sorting strings:

res = sorted(yoy_dict.items(), key=lambda x: float(x[1][:-1]), reverse=True)

Result:

print(res)

[('HOUGANG', '1.130759%'),
 ('JURONG EAST', '0.786807%'),
 ('PUNGGOL', '0.238738%'),
 ('BUKIT BATOK', '-0.296952%'),
 ('YISHUN', '-0.843832%'),
 ('JURONG WEST', '-1.037612%'),
 ('CENTRAL AREA', '-1.266556%'),
 ('MARINE PARADE', '-1.445532%'),
 ('SENGKANG', '-1.548278%'),
 ('CHOA CHU KANG', '-1.923021%'),
 ('WOODLANDS', '-2.043103%'),
 ('SEMBAWANG', '-2.150383%')]

Answer 2

It seems that your problem is due to the usage of strings instead of numbers for storing percentage values. You need to convert strings to floats.

 key=lambda x: float(x[1][:-1])

Note:

10 > 9  # True
'10' > '9'  # False

It's because strings are being compared one character in time. When Python finds the first different characters in two strings, it chooses the biggest and stops here.