Why does my python dict become unordered?

Question

I am using this to produce a plot of % of names starting with a certain letter over a span of years. When plotting (and printing) my diction (letter_d) the keys are disordered rather than being sequential like how they are added to the dict. Is there a way to fix this, I believe I am adding them to the dict in a sequential order. If not is there a way I can create connect the dots of my scatter plot in order to simulate the correct line plot?

import csv
import matplotlib.pyplot as plt 

start = 1880
stop = 1890
x = []
years = range(start, stop +1)
print years
letter_d = {}
year_d = {}
alphabet = ['Z']#,'C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z']

for i in alphabet:
    letter_d[i] = 0

for year in years:
    filename = 'yob' + str(year) + '.txt'
    z = open(filename)      
    year_d[int(year)] = 0
    letter_d[i] = year_d
    c = 0
    d = 0
    for line in z:
        y = line.strip().split(',')
        y.remove(y[1])
        c += int(y[1])
        if i in y[0]:
            d += int(y[1])
        year_d[year] = float(d)/float(c)            
        #x.append(y)
#print year_d
print year_d.keys()
plt.plot(year_d.keys(), year_d.values())
plt.show()

Python dictionaries are **always** unordered. – Martijn Pieters Feb 08 '14 at 19:56 — Martijn Pieters, Feb 08 '14 at 19:56
Use `OrderedDict` from `collections`. – Feb 08 '14 at 19:57 — , Feb 08 '14 at 19:57

score 6 · Answer 1 · edited May 24 '16 at 07:46

6

Python dictionaries are always unordered.

In your case, you don't need a dictionary at all. Use two lists; one is the years list you already produced from a range, the other for the calculated values:

year_values = []

for year in years:
    # ...
    year_values.append(float(d)/float(c))

plt.plot(years, year_values)

edited May 24 '16 at 07:46

Marco Bonelli

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answered Feb 08 '14 at 19:59

Martijn Pieters

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That makes my work much clearer, thank you. – cubedNnoobed Feb 08 '14 at 20:58

score 1 · Answer 2 · answered Feb 08 '14 at 21:20

As it was said dictionaries are unordered. To keep your code, there is a way to display your plot sorted. Sorting dictionary keys.

Look

if __name__ == "__main__":
    year_d = {"5": 'b', "3": 'c', "4": 'z', "1":'a'}
    print year_d.keys()
    keys = map(int, year_d.keys())
    keys = map(keys.sort(), keys)
    print keys

original: ['1', '3', '5', '4'] sorted: [1, 3, 4, 5]

Why does my python dict become unordered?

2 Answers2

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