Join two python arrays via index

Question

i have a problem in Python. I am creating two numpy arrays from dict entries. I want to join those two numpy arrays in a specific way like this:

# create array with classes
probVec = filePickle['classID']
a = np.empty([0, 1])

for x in np.nditer(probVec):
    a = np.append(a,x)

timeVec = filePickle['start']
timeVec = np.asarray(timeVec)
b = np.empty([0, 1])

for x in np.nditer(timeVec):
    b = np.append(b,x)

# create input-vectors for clustering
c = np.vstack((b,a)).transpose()

Now, if i want to join them in a more specific way, like taking only specific items of array "probVec" to join them with the corresponding entry of array "timeVec" like this:

for x in np.nditer(probVec):
    if x == 3.0:
        a = np.append(a,x)

for x in np.nditer(timeVec):
    b = append with x values that have the same indices as the ones appended in the first loop

Because both arrays contain values corresponding to each other they have the same length. So my goal is something like this:

probVec = [2.0, 1.0, 3.0, 3.0, 4.0, 3.0...]

timeVec = [t1, t2, t3, t4, t5, t6...]

c = [[3.0 t3]
     [3.0 t4]
     [3.0 t6]
         .
         .
         .
     ]

I just don't know what's the best way to realize that.

Sammelsurium · Accepted Answer · 2016-01-05 02:27:12Z

1

Using a comparison operator on an array, like a == 3.0, you get a boolean array that can be used for indexing, selecting the rows where the condition is true.

In [87]: a = np.random.randint(low=1, high=4, size=10)   # example data

In [88]: a
Out[88]: array([3, 1, 3, 1, 1, 3, 2, 2, 2, 2])

In [89]: b = np.arange(10)

In [90]: c = np.column_stack((a, b))

In [91]: c[a == 3]
Out[91]: 
array([[3, 0],
       [3, 2],
       [3, 5]])

answered Jan 5, 2016 at 2:27

Sammelsurium

5163 silver badges6 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Join two python arrays via index

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related