：在python 3.1中显示多维数组中的所有元素

Question

I have a multidimensional array in python like:

arr = [['foo', 1], ['bar',2]]

Now, if I want to print out everything in the array, I could do:

print(arr[:][:])

Or I could also just do print(arr). However, If I only wanted to print out the first element of each box (for arr, that would be 'foo', 'bar'), I would imagine I would do something like:

print(arr[:][0])

however, that just prints out the first data blog (['foo', 1]), also, I tried reversing it (just in case):

print(arr[0][:])

and I got the same thing. So, is there anyway that I can get it to print the first element in each tuple (other than:

for tuple in arr:
    print(tuple[0])

)? Thanks.

Answer 1

You can transpose the array, eg

>>> list(zip(*arr))[0]
('foo', 'bar')

Answer 2

zip() will be a little slower than your original solution. If you don't like your original solution because it requires multiple lines of code you can always do this:

[i[0] for i in arr]

zip() has a for loop inside so you cannot be faster than a for loop using zip().

Answer 3

I think there might be a misunderstanding about how python parses the indexing. You can tack as many [:] onto the array as you like and you'll get the same thing back.

>>> arr = [['foo', 1], ['bar',2]]
>>> print arr[:][:][:][:]
[['foo', 1], ['bar', 2]]

The second [] only indexes into the second dimension when you return an actual list-like object. It sounds like you want Matlab syntax like arr[:,0] which you'll need to use something like numpy.