Day 29 [Python ML、资料清理] 处理输入资料不一致

Get our environment set up

# modules we'll use
import pandas as pd
import numpy as np

# helpful modules
import fuzzywuzzy
from fuzzywuzzy import process
import chardet

# read in all our data
professors = pd.read_csv("./pakistan_intellectual_capital.csv")

# set seed for reproducibility
np.random.seed(0)

/opt/conda/lib/python3.6/site-packages/fuzzywuzzy/fuzz.py:11: UserWarning: Using slow pure-python SequenceMatcher. Install python-Levenshtein to remove this warning
  warnings.warn('Using slow pure-python SequenceMatcher. Install python-Levenshtein to remove this warning')

Do some preliminary text pre-processing

我们快速的看过资料

professors.head()

我们现在先看Country这个column中，有没有哪边有资料不一致的问题

# get all the unique values in the 'Country' column
countries = professors['Country'].unique()

# sort them alphabetically and then take a closer look
countries.sort()
countries

array([' Germany', ' New Zealand', ' Sweden', ' USA', 'Australia',
       'Austria', 'Canada', 'China', 'Finland', 'France', 'Greece',
       'HongKong', 'Ireland', 'Italy', 'Japan', 'Macau', 'Malaysia',
       'Mauritius', 'Netherland', 'New Zealand', 'Norway', 'Pakistan',
       'Portugal', 'Russian Federation', 'Saudi Arabia', 'Scotland',
       'Singapore', 'South Korea', 'SouthKorea', 'Spain', 'Sweden',
       'Thailand', 'Turkey', 'UK', 'USA', 'USofA', 'Urbana', 'germany'],
      dtype=object)

从资料中我们可以看出有一些不一致的问题，例如:Germany、germany, New Zealand、New Zealand

第一步是要先将所有资料转为小写，并且将空格移除掉

在文本数据中，大写和空格的问题非常常见，这样处理过後，可以修复80%以上的不一致问题

# convert to lower case
professors['Country'] = professors['Country'].str.lower()
# remove trailing white spaces
professors['Country'] = professors['Country'].str.strip()

然後我们来处理更困难的不一致问题

Use fuzzy matching to correct inconsistent data entry

然後我们现在来看一下前面处理过後的资料

# get all the unique values in the 'Country' column
countries = professors['Country'].unique()

# sort them alphabetically and then take a closer look
countries.sort()
countries

array(['australia', 'austria', 'canada', 'china', 'finland', 'france',
       'germany', 'greece', 'hongkong', 'ireland', 'italy', 'japan',
       'macau', 'malaysia', 'mauritius', 'netherland', 'new zealand',
       'norway', 'pakistan', 'portugal', 'russian federation',
       'saudi arabia', 'scotland', 'singapore', 'south korea',
       'southkorea', 'spain', 'sweden', 'thailand', 'turkey', 'uk',
       'urbana', 'usa', 'usofa'], dtype=object)

现在又有出现其他的不一致，例如说south korea、southkorea

我们将会使用fuzzywuzzy套件来帮助我们确定那些字符彼此是接近的，只要数据集够小，就可以很好的纠正错误。

Fuzzy mathcing:自动寻找非常相似的字串的过程，称为Fuzzy matching。这个方法没办法100%的解决问题，但是至少可以节省一些时间

Fuzzywuzzy会返回两个字串之间的比例，比例越接近100，就代表说两个字串越相向

# get the top 10 closest matches to "south korea"
matches = fuzzywuzzy.process.extract("south korea", countries, limit=10, scorer=fuzzywuzzy.fuzz.token_sort_ratio)

# take a look at them
matches

[('south korea', 100),
 ('southkorea', 48),
 ('saudi arabia', 43),
 ('norway', 35),
 ('ireland', 33),
 ('portugal', 32),
 ('singapore', 30),
 ('netherland', 29),
 ('macau', 25),
 ('usofa', 25)]

从上面的结果可以看出，south korea和southkorea是非常接近的，我们将相似程度>47的资料替换成south korea

我们将这个步骤写成一个function，比较方便後续的处理

# function to replace rows in the provided column of the provided dataframe
# that match the provided string above the provided ratio with the provided string
def replace_matches_in_column(df, column, string_to_match, min_ratio = 47):
    # get a list of unique strings
    strings = df[column].unique()
    
    # get the top 10 closest matches to our input string
    matches = fuzzywuzzy.process.extract(string_to_match, strings, 
                                         limit=10, scorer=fuzzywuzzy.fuzz.token_sort_ratio)

    # only get matches with a ratio > 90
    close_matches = [matches[0] for matches in matches if matches[1] >= min_ratio]

    # get the rows of all the close matches in our dataframe
    rows_with_matches = df[column].isin(close_matches)

    # replace all rows with close matches with the input matches 
    df.loc[rows_with_matches, column] = string_to_match
    
    # let us know the function's done
    print("All done!")

# use the function we just wrote to replace close matches to "south korea" with "south korea"
replace_matches_in_column(df=professors, column='Country', string_to_match="south korea")

All done!

# get all the unique values in the 'Country' column
countries = professors['Country'].unique()

# sort them alphabetically and then take a closer look
countries.sort()
countries

array(['australia', 'austria', 'canada', 'china', 'finland', 'france',
       'germany', 'greece', 'hongkong', 'ireland', 'italy', 'japan',
       'macau', 'malaysia', 'mauritius', 'netherland', 'new zealand',
       'norway', 'pakistan', 'portugal', 'russian federation',
       'saudi arabia', 'scotland', 'singapore', 'south korea', 'spain',
       'sweden', 'thailand', 'turkey', 'uk', 'urbana', 'usa', 'usofa'],
      dtype=object)

将资料替换过後再过来检查，确认资料已经被替换了