How to compare the first element with others in numpy?-CodePudding

I'm trying to get an array where it shows whether each of the element equals to the first element in every row:

a = np.array([[1,2,1],[3,3,3],[2,0,1]])
b = a[:,0] == a[:]
print(b)

In 1st row should check 1 == 1, 1 == 2, 1 == 1.

In 2nd row should check 3 == 3, 3 == 3, 3 == 3.

In 3rd row should check 2 == 2, 2 == 0, 2 == 1.

However the output it wrong:

array([[ True, False, False],
       [False,  True, False],
       [False, False, False]])

Should be:

array([[ True, False,  True],
       [ True,  True,  True],
       [ True, False, False]])

Now what am I doing wrong and how to get the correct result?

CodePudding user response：

To brodcast you need to reshape to add an extra dimension:

a[:,0,None] == a

Output:

array([[ True, False,  True],
       [ True,  True,  True],
       [ True, False, False]])