pandas常用语法

常见的一些pandas的使用方法

import pandas as pd

food_info = pd.read_csv('food_info.csv')
print(type(food_info))
print(food_info.dtypes)
# print(help(pd.read_csv))

# 显示前3行 food_info.head(3)
print(food_info.head())
first_rows = food_info.head()
print(first_rows)
food_info.tail(3)

# 显示每一列的列名
print(food_info.columns)
print(food_info.shape)

# 取数据,用索引来取数据, loc[]
print(food_info.loc[0])
# 也可以通过切片取数据
print(food_info.loc[3:6])
# Return a DataFrame containing the rows at index 2, 5, 10
two_five_ten = [2, 5, 10]
print(food_info.loc[two_five_ten])

# 取XX列数据
ndb_col = food_info['NDB_No']
print(ndb_col)
# col_name = 'NDB_No'
# print(food_info[col_name])
columns = ['Zinc_(mg)', 'copper_(mg)']
print(food_info[columns])

# 写一个简单的代码, 把以g结尾的列名找出来
col_names = food_info.columns.tolist()
print(col_names)
gram_columns = []

for c in col_names:
    if c.endswith('(g)'):
        gram_columns.append(c)
gram_df = food_info[gram_columns]
print(gram_df.head(3))

# pandas 进行数学运算, 对每一个值都进行相同的操作
print(food_info['Iron_(mg)'])
div_1000 = food_info['Iron_(mg)'] / 1000
print(div_1000)

# 对维度相同的列进行组合, 就是对应位置的操作
water_energy = food_info['Water_(g)'] * food_info['Energ_Kcal']
print(water_energy)

# 对应维度增加一列
iron_grams = food_info['Iron_(mg)'] / 1000
food_info['Iron_(g)'] = iron_grams
print(food_info.shape)

# 常见的函数
max_calories = food_info['Energ_Kcal'].max()
# 归一化操作Divide the values
normalized_calories = food_info['Energ_Kcal'] / max_calories
food_info["normalized_cal"] = normalized_calories

# 排序的操作
food_info.sort_values('sodium_(mg)', inplace=True)
print(food_info['sodium_(mg)'].head(20))
# 降序
food_info.sort_values('sodium_(mg)', inplace=True, ascending=False)
print(food_info['sodium_(mg)'].head(20))

import pandas as pd
import numpy as np

titanic_survival = pd.read_csv('titanic_train.csv')
print(titanic_survival.head())

# 对缺失值进行补充
age = titanic_survival['Age']
print(age.loc[0:10])
age_is_null = pd.isnull(age)
print(age_is_null)
age_null_true = age[age_is_null]
print(age_null_true)

age_null_count = len(age_null_true)
print(age_null_count)
# 缺失值进行处理
mean_age = sum(titanic_survival['Age']) / len(titanic_survival['Age'])
print(mean_age)

good_ages = titanic_survival['Age'][age_is_null == False]
print(good_ages)
correct_mean_age = sum(good_ages) / len(good_ages)
print(correct_mean_age)

# 也可以直接通过调用.mean()
correct_mean_age = titanic_survival['Age'].mean()
print(correct_mean_age)

# mean fare for each class
passenger_class = [1, 2, 3]
fares_by_class = {}
for this_class in passenger_class:
    pclass_rows = titanic_survival[titanic_survival['Pclass'] == this_class]
    pclass_fares = pclass_rows['fare']
    fares_for_class = pclass_fares.mean()
    fares_by_class[this_class] = fares_for_class

print(fares_by_class)

# 快速进行数据统计
'''
index = which columns group by
values is the columns we want to calculate
'''
passenger_survival = titanic_survival.pivot_table(index='Pclass', values='Survived', aggfunc=np.mean)
print(passenger_survival)

passenger_class = titanic_survival.pivot_table(index='Pclass', values='fare', aggfunc=np.mean)
print(passenger_class)

passenger_age = titanic_survival.pivot_table(index='Pclass', values='Age', aggfunc=np.mean)
print(passenger_age)

port_stats = titanic_survival.pivot_table(index='Embarked', values=['fare', 'Survived'], aggfunc=np.sum)
print(port_stats)

# 把缺失值全部删除,
drop_na_columns = titanic_survival.dropna(axis=1)
print(drop_na_columns)
# 删除样本
new_titanic_survival = titanic_survival.dropna(axis=0, subset=['Age', 'Sex'])
print(new_titanic_survival)

# 取某一个特殊的值
row_index_83_age = titanic_survival.loc[83, 'Age']
print(row_index_83_age)

# 排序, 然后重置索引
new_titanic_survival = titanic_survival.sort_values('Age', ascending=False)
print(new_titanic_survival[0:10])

titanic_reindexed = new_titanic_survival.reset_index(drop=True)
print('------')
print(titanic_reindexed.loc[0:10])

# pandas 自定义函数 apply
def hundredth_row(column):
    # extract the hundredth item
    hundredth_item = column.loc[99]
    return hundredth_item

# Return
hundredth_row = titanic_survival.apply(hundredth_row)
print(hundredth_row)

def not_null_count(column):
    column_null = pd.isnull(column)
    null = column[column_null]
    return len(null)

column_null_count = titanic_survival.apply(not_null_count)
print(column_null_count)

# 改变仓位等级
def which_class(row):
    pclass = row['Pclass']
    if pd.isnull(pclass):
        return 'UnkNown'
    elif pclass == 1:
        return 'First Class'
    elif pclass == 2:
        return  'Second Class'
    elif pclass == 3:
        return 'Third Class'
classes = titanic_survival.apply(which_class, axis=1)
print(classes)

# 年龄离散化
def is_minor(row):
    if row['Age'] < 18:
        return True
    else:
        return False

minors = titanic_survival.apply(is_minor, axis=1)
print(minors)

def generate_age_label(row):
    age = row['Age']
    if pd.isnull(age):
        return 'UnkNown'
    elif age < 18:
        return 'minor'
    else:
        return 'adult'
age_label = titanic_survival.apply(generate_age_label, axis=1)
print(age_label)

titanic_survival['age_labels'] = age_label
age_group_survival = titanic_survival.pivot_table(index='age_labels', values='Survived')
print(age_group_survival)

# Series 结构
# Dataframe (collection of Series objects)
# A Series object can hold many data type
import pandas as pd
fangango = pd.read_csv("fandango_scores.csv")
series_film = fangango['FILM']
print(type(series_film))
print(series_film[0:5])
series_rt = fangango['RottenTomatoes']
print(series_rt[0:5])

# 改变Series索引
from pandas import Series

film_names = series_film.values
print(type(film_names))
print(film_names)
print('------')
rt_scores = series_rt.values
print(rt_scores)

series_custom = Series(rt_scores, index=film_names)
print(series_custom[['Minions (2015)', 'Max (2015)']])
fiveten = series_custom[5:10]
print(fiveten)

# 排序
original_index = series_custom.index.tolist()
print(original_index)
sorted_index = sorted(original_index)
sort_by_index = series_custom.reindex(sorted_index)
print(sort_by_index)

sc2 = series_custom.sort_index()
sc3 = series_custom.sort_values()
print(sc2[0:10])
print(sc3[0:10])

# Series 相加 和常见函数
import numpy as np
print(np.add(series_custom, series_custom))
np.sin(series_custom)
np.max(series_custom)

# 条件表达式
print(series_custom > 50)
series_greater_than_50 = series_custom[series_custom > 80]
print(series_greater_than_50)

# index 相同, 可以直接计算
rt_citics = Series(fangango['RottenTomatoes'].values, index=fangango['FILM'])
rt_users = Series(fangango['RottenTomatoes_User'].values, index=fangango['FILM'])
rt_mean = (rt_citics + rt_users) / 2
print(rt_mean)

# DataFrame 也可以指定索引
fangango_films = fangango.set_index('FILM', drop=False)
print(fangango_films)

# 如果索引不是数字, 也可以用切片, loc
print(fangango_films['Avengers: Age of Ultron (2015)':'Hot Tub Time Machine 2 (2015)'])
print(fangango_films.loc['Avengers: Age of Ultron (2015)':'Hot Tub Time Machine 2 (2015)'])

# 利用匿名函数, apply
types = fangango_films.dtypes
print(types)
float_columns = types[types.values == 'float64'].index
float_df = fangango_films[float_columns]
print(float_df)
rt_mt_user = float_df.apply(lambda x: np.std(x))
print(rt_mt_user)