Append x 第一次出现在列表中并中断循环。 但是，如果 y 出现在 x 之前，append y 第一次出现，则忽略 y 直到 x 第一次出现

Question

I am iterating through a column in multiple dataframes df1['values'] , df2['values'] , and so on. The elements in ['values'] look like this:

[3, 1, 3, 1, 1, 4, 4, 3, 3, 1, 2, 1, 1, 3, 4, 2, 3, 1, 1, 1]

I want to loop through the column and append the first occurrence of 4 to a new list and break the loop. However, if 3 occurs before 4, then I want to append that 1st occurrence of 3, ignore any subsequent occurrence of 3, but continue looping until I get to the first occurrence of 4, then break the loop.

So, with the list above: [3, 1, 3, 1, 1, 4, 4, 3, 3, 1, 2, 1, 1, 3, 4, 2, 3, 1, 1, 1]

Desired output would be: [3,4]

But if the list looked like: [2, 1, 2, 1, 1, 4, 4, 3, 3, 1, 2, 1, 1, 3, 4, 2, 3, 1, 1, 1]

Desired output would be: [4]

Answer 1

You could do it like this:

u = df['values'].unique()
u = u[u >= 3]
u = u[:(u == 4).argmax()+1]

Output (using first list):

>>> u
array([3, 4])

Output (using second list):

>>> u
array([4])