Pandas，使用 for 循环构建新的数据框
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Pandas, build new dataframe with for loop
提问by jonas
I have a really simple problem that I cant solve in Pandas. I have a dataframe to start with, with that dataframe I want to apply some function. I want to repeat this many times and build/stack the reults from the operations in a new larger dataframe. I was thinking of doing this with a for loop. Here is a simplified example that I can not get to work:
我有一个非常简单的问题，我无法在 Pandas 中解决。我有一个数据框开始，我想用这个数据框应用一些功能。我想多次重复这一点，并在一个新的更大的数据帧中构建/堆叠操作的结果。我想用 for 循环来做这件事。这是一个我无法开始工作的简化示例：
import pandas as pd
df = pd.DataFrame(np.random.randn(3, 4), columns=list('ABCD'))
large_df = df*0
for i in range(1,10):
df_new = df*i
large_df= pd.concat(large_df,df_new)
large_df
Any ideas??
有任何想法吗？？
回答by Dan Allan
It will be fastest to build all of the results first and concatenate once in the end. If you append one result at a time, the memory for the results has to be re-allocated each time.
首先构建所有结果并最终连接一次将是最快的。如果一次添加一个结果，则每次都必须重新分配结果的内存。
So, if you are applying some_functionwith a different parameter pthrough the loop (like iin your toy example above) I suggest:
因此，如果您通过循环应用some_function不同的参数p（如i上面的玩具示例），我建议：
pd.concat([df.apply(lambda x: some_function(x, p)) for p in parameters])
