Python 如何从熊猫数据框中的当前行中减去前一行并将其应用于每一行；不使用循环？
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How do I subtract the previous row from the current row in a pandas dataframe and apply it to every row; without using a loop?
提问by ZacAttack
I am using Python3.5 and I am working with pandas. I have loaded stock data from yahoo finance and have saved the files to csv. My DataFrames load this data from the csv. This is a copy of the ten rows of the csv file that is my DataFrame
我正在使用 Python3.5，并且正在使用 Pandas。我已经从雅虎财经加载了股票数据并将文件保存到 csv。我的 DataFrames 从 csv 加载这些数据。这是作为我的 DataFrame 的 csv 文件的十行的副本
Date Open High Low Close Volume Adj Close
1990-04-12 26.875000 26.875000 26.625 26.625 6100 250.576036
1990-04-16 26.500000 26.750000 26.375 26.750 500 251.752449
1990-04-17 26.750000 26.875000 26.750 26.875 2300 252.928863
1990-04-18 26.875000 26.875000 26.500 26.625 3500 250.576036
1990-04-19 26.500000 26.750000 26.500 26.750 700 251.752449
1990-04-20 26.750000 26.875000 26.750 26.875 2100 252.928863
1990-04-23 26.875000 26.875000 26.750 26.875 700 252.928863
1990-04-24 27.000000 27.000000 26.000 26.000 2400 244.693970
1990-04-25 25.250000 25.250000 24.875 25.125 9300 236.459076
1990-04-26 25.000000 25.250000 24.750 25.000 1200 235.282663
I know that I can use iloc, loc, ix but these values that I index will only give my specific rows and columns and will not perform the operation on every row. For example: Row one of the data in the open column has a value of 26.875 and the row below it has 26.50. The price dropped .375 cents. I want to be able to capture the % of Increase or Decrease from the previous day so to finish this example .375 divided by 26.875 = 1.4% decrease from one day to the next. I want to be able to run this calculation on every row so I know how much it has increased or decreased from the previous day. The index functions I have tried but they are absolute, and I don't want to use a loop. Is there a way I can do this with the ix, iloc, loc or another function?
我知道我可以使用 iloc、loc、ix，但是我索引的这些值只会给出我的特定行和列，并且不会对每一行执行操作。例如：打开列中数据的第一行值为 26.875，其下方的行值为 26.50。价格下跌了 0.375 美分。我希望能够捕获前一天的增加或减少百分比，以便完成此示例，0.375 除以 26.875 = 1.4% 从一天到下一天减少。我希望能够在每一行上运行这个计算，这样我就知道它比前一天增加了多少或减少了多少。我尝试过的索引函数但它们是绝对的，我不想使用循环。有没有办法用 ix、iloc、loc 或其他函数来做到这一点？
回答by MaxU
you can use pct_change()or/and diff()methods
您可以使用pct_change()或/和diff()方法
Demo:
演示：
In [138]: df.Close.pct_change() * 100
Out[138]:
0 NaN
1 0.469484
2 0.467290
3 -0.930233
4 0.469484
5 0.467290
6 0.000000
7 -3.255814
8 -3.365385
9 -0.497512
Name: Close, dtype: float64
In [139]: df.Close.diff()
Out[139]:
0 NaN
1 0.125
2 0.125
3 -0.250
4 0.125
5 0.125
6 0.000
7 -0.875
8 -0.875
9 -0.125
Name: Close, dtype: float64
