python 数据类型list、dict、numpy array、series、dataframe之间的转换

引言

dataframe是pandas的数据类型；

ndarray是numpy的数据类型；

list和dict是python的数据类型；

series是pandas的一种数据类型，Series是一个定长的，有序的字典，因为它把索引和值映射起来了。

通过以下例子，可以更加清楚它们的数据表示。

1. list to others

import numpy as np
import pandas as pd
from pandas import Series, DataFrame

# list
data = [[2000, 'Ohino', 1.5],[2001, 'Ohino', 1.7],[2002, 'Ohino', 3.6],[2001, 'Nevada', 2.4],[2002, 'Nevada', 2.9]]  # type(data) 为 list# list to series
ser = Series(data, index = ['one', 'two', 'three', 'four', 'five'])# list to dataframe
df = DataFrame(data, index = ['one', 'two', 'three', 'four', 'five'], columns = ['year', 'state', 'pop'])# list to array
ndarray = np.array(data)

运行结果：

# Series
one       [2000, Ohino, 1.5]
two       [2001, Ohino, 1.7]
three     [2002, Ohino, 3.6]
four     [2001, Nevada, 2.4]
five     [2002, Nevada, 2.9]
dtype: object
# dataframeyear   state  pop
one    2000   Ohino  1.5
two    2001   Ohino  1.7
three  2002   Ohino  3.6
four   2001  Nevada  2.4
five   2002  Nevada  2.9
# ndarray
[['2000' 'Ohino' '1.5']['2001' 'Ohino' '1.7']['2002' 'Ohino' '3.6']['2001' 'Nevada' '2.4']['2002' 'Nevada' '2.9']]

2. ndarray to others

# array to dataframe
pd = DataFrame(ndarray, index = ['one', 'two', 'three', 'four', 
'five'], 
columns = ['year', 'state', 'pop'])

# ndarray to list
mylist = ndarray.tolist()

3. dict to others

import numpy as np
import pandas as pd
from pandas import Series, DataFrame# dict
data = {
     'name': ['Li', 'Zhang', 'Wang'],'year': [2000, 2001, 2002]}  # type(data) 为 dict

# dict to series
# 若不指定 index，data 的 key 充当 Series 的 index
ser = Series(data)
print('ser\n', ser)# dict to dataframe
# 若不指定 columns，data 的 key 充当 DataFrame 的 columns
df = DataFrame(data)
print('df\n', df)

4. Series to others

如果把DataFrame取一列就是Series格式了。

# series to np array
# 需要pandas version 0.24以上
arr = ser.to_numpy()
# 或者
arr = np.array(ser)
# Series转换成dict
dt = ser.to_dict()

5. DataFrame to others

# dataframe
data = DataFrame(np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]]), columns=['a', 'b', 'c'])
print(data)# dataframe to array
arr = data.values
print('arr\n', arr)
print(type(arr))# dataframe to dict 
dict = data.to_dict()
print(dict)

DataFrame.to_dict(self, orient='dict', into=<class 'dict'>) 还可以转换成 list,series等：

 orient : str {
    ‘dict’, ‘list’, ‘series’, ‘split’, ‘records’, ‘index’}
Determines the type of the values of the dictionary.‘dict’ (default) : dict like {
    column -> {
    index -> value}}
‘list’ : dict like {
    column -> [values]}
‘series’ : dict like {
    column -> Series(values)}
‘split’ : dict like {
    ‘index’ -> [index], ‘columns’ -> [columns], ‘data’ -> [values]}
‘records’ : list like [{
    column -> value}, … , {
    column -> value}]
‘index’ : dict like {
    index -> {
    column -> value}}
Abbreviations are allowed. s indicates series and sp indicates split.

最近开通了个公众号，主要分享python原理与应用，推荐系统，风控等算法相关的内容，感兴趣的伙伴可以关注下。

公众号相关的学习资料会上传到QQ群596506387，欢迎关注。

参考：

1. Yam_ List, Dict, Array, Series, DataFrame 相互转换;
2. dataframe to_dict() ;
3. pandas dataframe;
4. pandas Series;