Append 1st occurence of x to a list and break loop. However, if y occurs before x, append 1st occurr-CodePudding

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]

CodePudding user response：

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])