CODEWITHSUNDEEP
pythonnumpy
n3o
n3o

Reputation: 67

Scalar Multipliction Numpy

I need to multiply a scalar value to a numpy array starting from a specific element.

eg) 3 * [1,1,1,1,1,1] = [1,3,3,3,3,3]

I have tried to do np.dot(value, arr[1:]), but this removes the first element. How would I do this?

Upvotes: 2

Views: 102

Answers (2)

Lukas S
Lukas S

Reputation: 3603

arr = np.array([1,1,1,1])
arr[1:] *= 2

or

arr = np.array([1,1,1,1])
arr[1:] = 2*arr[1:]

gives

arr->array([1, 2, 2, 2])

Upvotes: 2

Quang Hoang
Quang Hoang

Reputation: 150785

Is your data a numpy array or a python array? For numpy array:

a[1:] *= 3

For python array:

for i in range(1,len(a)): a[i] *= 3

Note: Of course the python approach works for numpy arrays as well, but it wouldn't take advantage of numpy's vectorization.

Upvotes: 4

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