CODEWITHSUNDEEP
pythonpython-3.xnumpymatrix
misheekoh
misheekoh

Reputation: 460

Inserting/Adding/Updating elements in matrix

Let's say I've initialized a matrix/array that has 400 rows, 3 columns:

distances = np.zeros([400, 3], dtype=np.float64)

Now, I have a for loop that returns 1200 objects (float values) and I want to "append" each element into distances (row by row) or assign those float values to each element in the matrix like:

distances[0,1] = item1,
distances[0,2] = item2, 
distances[0,3] = item3, 
distances[1,1] = item4,
distances[1,2] = .....

How can I do this? I tried numpy.append and numpy.insert but I failed. Any ideas?

Upvotes: 0

Views: 48

Answers (2)

dawg
dawg

Reputation: 104102

If you want random access, you can do it with enumeration (to get row by row access) and slice assignment:

distances = np.zeros([400, 3], dtype=np.float64)

start=[1,2,3]
for i,_ in enumerate(distances):
    distances[i][:]=start
    start=[x+1 for x in start]
>>> distances
[[   1.    2.    3.]
 [   2.    3.    4.]
 [   3.    4.    5.]
 ..., 
 [ 398.  399.  400.]
 [ 399.  400.  401.]
 [ 400.  401.  402.]]

Upvotes: 1

Mike Müller
Mike Müller

Reputation: 85612

Gather you items in a list, convert this list into NumPy array and reshape:

distances = np.array([item1, item2, ... item1200], dtype=float).reshape((400, 3))

Upvotes: 1

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