从发电机列表创建 pandas 数据框 [英] Create Pandas Dataframe from List of Generators
问题描述
我要问以下问题。有没有一种方法可以从python Generator对象列表中构建DataFrame。我使用列表推导来创建包含数据帧数据的列表:
data_list.append([record.Timestamp,record.Value ,record.Name,record.desc]记录中的记录)
我这样做是因为正常for循环中的list append花费的时间大约是20倍:
用于记录中的记录:
data_list.append( record.Timestamp,record.Value,record.Name,record.desc)
我试图创建数据框,但不起作用:
此:
数据框= pd.DataFrame(data_list,columns = ['timestamp','value','name','desc'])
抛出异常:
ValueError:传递了4列,传递的数据有142538列。
我也尝试使用以下itertools:
dataframe = pd.DataFrame(data =([[list(elem)for itm.chai中的elem n.from_iterable(data_list)]),columns = ['timestamp','value','name','desc'])
结果为空的DataFrame:
Empty DataFrame\nColumns:[时间戳,值,名称, desc] \nIndex:[]
data_list看起来像这样:
<$ p<发电机对象St ... 51DB0><发电机对象St ... 56EB8><发电机对象St ... 51F10><发电机对象St. ..51F68>]
用于生成列表的代码如下:
用于events_list中的事件:
用于事件中的记录:
data_list.append([record.Timestamp,record.Value,record。记录中的记录的名称,record.desc]
由于事件列表数据结构的缘故,这是必需的。
我是否可以通过生成器列表来创建数据框?如果有,那将节省时间吗?我的意思是,我用列表理解替换普通的for循环节省了很多时间,但是,如果创建数据框需要更多时间,则此操作将毫无意义。
只需将您的 data_list
转换为生成器表达式。例如:
从集合中导入namedtuple
MyData = namedtuple( MyData,[ a ])
data =(da在(MyData(i)在范围(100)中为i的da中))
df = pd.DataFrame(data)
就可以了。因此,您应该做的是:
data =((record.Timestamp,record.Value,record.Name,record。 desc)记录中的记录)
df = pd.DataFrame(data,columns = [ Timestamp, Value, Name, Desc])
您的方法不起作用的实际原因是因为您在 data_list
中只有一个条目我想是142538条记录的生成器。熊猫会尝试将您的 data_list
中的单个条目填充到单行中(因此所有142538个条目,每个条目包含四个元素)都会失败,因为它期望4
编辑:您当然可以使生成器表达式更复杂,这是沿着事件的附加循环的示例:
从集合导入namedtuple
MyData = namedtuple( MyData,[ a, b])
数据=(对于范围(j)的j((da,db),对于范围(i)的i(MyData(j,j + i))(100)的d))
pd.DataFrame(data,columns = [ a, b])
编辑:这也是一个使用数据结构的示例,例如:
Record = namedtuple( Record,[ Timestamp, Value, Name, desc] )
event_list = [[Record(Timestamp = 1,Value = 1,Name = 1,desc = 1),
Record(Timestamp = 2,Value = 2,Name = 2, desc = 2)],
[Record(Timestamp = 3,Value = 3,N ame = 3,desc = 3)]]
data =((r.Timestamp,r.Value,r.Name,r.desc)对于event_list中的事件,对于r中的事件)
pd.DataFrame(data,columns = [ timestamp, value, name, desc])
输出:
时间戳记值名称desc
0 1 1 1 1
1 2 2 2 2
2 3 3 3 3
I have to following question. Is there a way to build a DataFrame from a list of python Generator objects. I used list comprehension to create the list with data for the dataframe:
data_list.append([record.Timestamp,record.Value, record.Name, record.desc] for record in records)
I did it this way because normal list append in a for loop is taking like 20x times longer:
for record in records:
data_list.append(record.Timestamp,record.Value, record.Name, record.desc)
I tried to create the dataframe but it doesn't work:
This:
dataframe = pd.DataFrame(data_list, columns=['timestamp', 'value', 'name', 'desc'])
Throws exception:
ValueError: 4 columns passed, passed data had 142538 columns.
I also tried to use itertools like this:
dataframe = pd.DataFrame(data=([list(elem) for elem in itt.chain.from_iterable(data_list)]), columns=['timestamp', 'value', 'name', 'desc'])
This results as a empty DataFrame:
Empty DataFrame\nColumns: [timestamp, value, name, desc]\nIndex: []
data_list looks like this:
[<generator object St...51DB0>, <generator object St...56EB8>,<generator object St...51F10>, <generator object St...51F68>]
Code for generating the list looks like this:
for events in events_list:
for record in events:
data_list.append([record.Timestamp,record.Value, record.Name, record.desc] for record in records)
This is required because of events list data structure.
Is there a way for me to create a dataframe out of list of Generators? If there is, is it going to be time efficient? What I mean is that I save a lot of time with replacing normal for loop with list comprehension, however if the creation of dataframe takes more time, this action will be pointless.
Just turn your data_list
into a generator expression as well. For example:
from collections import namedtuple
MyData = namedtuple("MyData", ["a"])
data = (d.a for d in (MyData(i) for i in range(100)))
df = pd.DataFrame(data)
will work just fine. So what you should do is have:
data = ((record.Timestamp,record.Value, record.Name, record.desc) for record in records)
df = pd.DataFrame(data, columns=["Timestamp", "Value", "Name", "Desc"])
The actual reason why your approach does not work is because you have a single entry in your data_list
which is a generator over - I suppose - 142538 records. Pandas will try to cram that single entry in your data_list
into a single row (so all the 142538 entries, each a list of four elements) and fails, since it expects rather 4 columns to be passed.
Edit: you can of course make the generator expression more complex, here's an example along the lines of your additional loop over events:
from collections import namedtuple
MyData = namedtuple("MyData", ["a", "b"])
data = ((d.a, d.b) for j in range(100) for d in (MyData(j, j+i) for i in range(100)))
pd.DataFrame(data, columns=["a", "b"])
edit: here's also an example using data structures like you are using:
Record = namedtuple("Record", ["Timestamp", "Value", "Name", "desc"])
event_list = [[Record(Timestamp=1, Value=1, Name=1, desc=1),
Record(Timestamp=2, Value=2, Name=2, desc=2)],
[Record(Timestamp=3, Value=3, Name=3, desc=3)]]
data = ((r.Timestamp, r.Value, r.Name, r.desc) for events in event_list for r in events)
pd.DataFrame(data, columns=["timestamp", "value", "name", "desc"])
Output:
timestamp value name desc
0 1 1 1 1
1 2 2 2 2
2 3 3 3 3
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