Check if item is in an array / list

问题:

If I've got an array of strings, can I check to see if a string is in the array without doing a for loop? Specifically, I'm looking for a way to do it within an if statement, so something like this:

if [check that item is in array]:

回答1:

Assuming you mean "list" where you say "array", you can do

if item in my_list:
    # whatever

回答2:

I'm also going to assume that you mean "list" when you say "array." Sven Marnach's solution is good. If you are going to be doing repeated checks on the list, then it might be worth converting it to a set or frozenset, which can be faster for each check. Assuming your list of strs is called subjects:

subject_set = frozenset(subjects)
if query in subject_set:
    # whatever

回答3:

Use a lambda function.

Let's say you have an array:

nums = [0,1,5]

Check whether 5 is in nums:

(len(filter (lambda x : x == 5, nums)) > 0)

---

This solution is more robust. You can now check whether any number satisfying a certain condition is in your array nums.

For example, check whether any number that is greater than or equal to 5 exists in nums:

(len(filter (lambda x : x >= 5, nums)) > 0)

回答4:

You have to use .values for arrays. for example say you have dataframe which has a column name ie, test['Name'], you can do

if name in test['Name'].values :
   print(name)

for a normal list you dont have to use .values

回答5:

You can also use the same syntax for an array. For example, searching within a Pandas series:

ser = pd.Series(['some', 'strings', 'to', 'query'])

if item in ser.values:
    # do stuff