How to find column b when column a equals a certain value in data frames python-CodePudding

I have a csv that contains user Ids movie Ids and ratings and I would like to return all of the movie ids for certain user ids. This is what the data looks like

 userId  movieId  rating   timestamp
    1        1     4.0   964982703
    1        3     4.0   964981247
    1        6     4.0   964982224
    1       47     5.0   964983815
    1       50     5.0   964982931

say I want to return all of the movies for user id 1 for example and store them in some sort of structure maybe a list. The output would be [1,3,6,47,50, … ].

I tried using this code just to print the outputs

for x in ratings["userId"]:
    for y in ratings["movieId"]:
        if x == 1:
            print(y)

but my output would just keep printing forever and forced vs code to shut down.

CodePudding user response：

You should loop on the same row:

for x in zip(ratings["userId"], ratings["movieId"]):
    if x == 1:
        print(y)

res = ratings.loc[ratings["userId"].eq(1),"movieId"].tolist()

CodePudding user response：

assuming userId is a string column, you can run:

print(ratings.query("userId == '1'")["movieId"])

otherwise, if it's an integer column, you can run:

print(ratings.query("userId == 1")["movieId"])