Number of values within a specific range in Python

I have an array T. I am trying to find the number of values within a specified range through T1 but I am getting an error. I present the expected output.

T=np.array([4.7,5.1,2.9])
T1=np.flatnonzero(2<T<3,3<T<4,4<T<5)
print(T1)

The error is

in <module>
    T1=np.flatnonzero(2<T<3,3<T<4,4<T<5)

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

The expected output is

T1=[1,0,1]

>Solution :

• flatnonzero has nothing to do with what you want.
• Furthermore, the error ‘The truth value of an array with more than one element is ambiguous’ comes from the double condition 2<T<3: you need to separate it into 2 conditions: (2<T) & (T<3).
• T[(2<T) & (T<3)] will yield an array of the values of T respecting the conditions.

Thus, if you need to count the elements of T that are between 2 and 3, you can do:

len(T[(2 <T) & (T < 3)])

To obtain what you want, you could then do this:

Ranges = [(2,3),(3,4),(4,5)]
T1 = [len(T[(a < T) & (T < b)]) for a,b in Ranges]

print(T1)
# [1, 0, 1]

To print the actual values fitting the criteria, you can do:

T2 = [list(T[(a < T) & (T < b)]) for a,b in Ranges]

print(T2)
# [[2.9], [], [4.7]]

To get the corresponding indices, we finally have a use for flatnonzero:

T3 = [list(np.flatnonzero((a < T) & (T < b))) for a,b in Ranges]

print(T3)
# [[2], [], [0]]