从数据框中减去特定列的每一行并添加到列表 -python

Question

I'm trying to subtract each ow of column A from DataFrame aa and add those to the list.

a = pd.DataFrame(np.random.randint(1,10,(5,4)),columns=['A','B','C','D']) list=[]

I am so sorry for this such a basic question but I can't find the solution.

Answer 1

Edit: Just realized you only wanted to extract a column from a DataFrame as a list. In that case, like @arkhadiusz commented, you can just use:

a.A.to_list()

Note that this won't remove the column from your DataFrame . If you'd like to completely remove it from your DataFrame , you can use:

a.pop('A').to_list()

---

Assuming you want to subtract a constant value from each element in a column of your DataFrame , you can try something like this:

x = 0.5 # some constant value you want to subtract
[val1 - val2 for val1, val2 in zip(a.A.to_list(), [x] * a.shape[0])]

Or if you want to subtract different values for each element, you can try:

x = [1, 2, 3, 4, 5]
[val1 - val2 for val1, val2 in zip(a.A.to_list(), x)]

Answer 2

If I understand correctly, you want this:

To get a numpy array:

lst = a[["B","C","D"]].subtract(a["A"], axis=0).values

To get a 2d list:

lst = a[["B","C","D"]].subtract(a["A"], axis=0).values.T.tolist()