[FIXED] Why does the pandas boolean mask not give me the desired result? What am I missing here?

Issue

all help appreciated on the following:

I have the following code implemented, which filters results from a pandas dataFrame in 4 steps:

mask =  ( (stock_hist['confirmed']== True) &\
    (stock_hist['prevday_confirmed'] == False) & \
     (stock_hist['nextday_confirmed'] == False) &\
         (stock_hist['nextday_above_supp'] == True) &\
             (stock_hist['prevday_above_supp'] == True)
         ) 
result1 = stock_hist[mask]    


mask = ( \
    (stock_hist['confirmed'] == True) & \
        (stock_hist['prevday_confirmed'] == False) & \
            (stock_hist['prevday_above_supp'] == True) &\
    (stock_hist['nextday_confirmed'] == True) & \
        (stock_hist['current_dist'] < stock_hist['nextday_dist']) \
            )          
result2 = stock_hist[mask]    

mask =  ( (stock_hist['confirmed']== True) &\
    (stock_hist['prevday_confirmed'] == True) & \
     (stock_hist['nextday_confirmed'] == False) &\
         (stock_hist['nextday_above_supp'] == True) &\
             (stock_hist['current_dist'] < stock_hist['prevday_dist'])
         ) 
result3 = stock_hist[mask]

mask =  ( (stock_hist['confirmed']== True) &\
    (stock_hist['prevday_confirmed'] == True) & \
     (stock_hist['nextday_confirmed'] == True) &\
         (stock_hist['current_dist'] < stock_hist['prevday_dist']) &\
             (stock_hist['current_dist'] < stock_hist['nextday_dist'])
         ) 
result4 = stock_hist[mask]


result = result1.append([result2, result3, result4])

                             

Now, this code does exactly what I expect it to do.

However, I would expect that I should be able to do this in one single mask, like so:

mask =  ( (stock_hist['confirmed']== True) &\
        ~(stock_hist['prevday_confirmed'] == False) & \
         ~(stock_hist['nextday_confirmed'] == False) &\
             ~(stock_hist['nextday_above_supp'] == True) &\
                 ~(stock_hist['prevday_above_supp'] == True) \
                     | \
        (stock_hist['confirmed'] == True) & \
            ~(stock_hist['prevday_confirmed'] == False) & \
                ~(stock_hist['prevday_above_supp'] == True) &\
        ~(stock_hist['nextday_confirmed'] == True) & \
            ~(stock_hist['current_dist'] < stock_hist['nextday_dist']) \
                | \
                    
                    :
                    :
                    :

But when I do that, it is as if the | acts as an & ? Because it renders FALSE for the entire mask, also for those rows that get filtered out succesfully with the first code....

What am i missing here?

Solution

This is a typical example of why the order of operations matters: just like 2 + 3 x 4 is not equal to (2 + 3) x 4, you need to add one more layer of parenthesis between your conditions.

(A & B | C & D) != ((A & B) | (C & D))

In your case, if of the mask has to be put between parenthesis in order to cumulate them in one condition using |

Answered By - Hugolmn