Error multiplying two numpy arrays

Question

I am getting an error that I don't quite understand with the following script. I thought I would be able to multiple the two numpy arrays happliy but I keep getting this error:

TypeError: unsupported operand type(s) for *: 'numpy.ndarray' and 'numpy.ndarray'

The script is below:

def currents_to_resistance(Istack1, Istack2, A_list, x_list):

    #Error Calcs
    Videal_R1 = (1.380648e-23 * (27+273.15)) / (1.6021766e-19)
    print Videal_R1
    Istack1 = np.array(Istack1)
    Istack2 = np.array(Istack2)
    print Istack1
    print Istack2   

    g = Istack1*Istack2
    print g

The print Istack1 Istack2 before the multiply come out as

['0.0005789047' '0.0005743839' '0.0005699334' '0.000565551' '0.0005612346'
 '0.0005569839' '0.0005527969' '0.0005486719' '0.000544608' '0.0005406044'
 '0.0005366572' '0.000532768' '0.000528934' '0.0005251549' '0.0005214295'
 '0.0005177562' '0.0005141338' '0.0005105614' '0.000507039' '0.0005035643'
 '0.0005001368' '0.0004967555' '0.0004934193' '0.0004901279' '0.0004868796'
 '0.0004836736']
['0.000608027' '0.0006080265' '0.0006080267' '0.0006080267' '0.0006080261'
 '0.0006080261' '0.0006080262' '0.0006080261' '0.0006080263' '0.0006080272'
 '0.0006080262' '0.0006080262' '0.0006080257' '0.0006080256' '0.0006080258'
 '0.0006080256' '0.0006080252' '0.0006080247' '0.000608025' '0.0006080249'
 '0.000608025' '0.0006080251' '0.0006080249' '0.0006080254' '0.0006080251'
 '0.0006080247']

I call the function using

Re_list = currents_to_resistance(full_list[i][0],full_list[i][1], temp_A, temp_x)

What am I missing here?

HYRY · Accepted Answer · 2012-05-08 03:55:58Z

6

convert string array to float array first:

Istack1 = np.array(Istack1, np.float)
Istack2 = np.array(Istack2, np.float)

answered May 8, 2012 at 3:55

HYRY

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Community · Accepted Answer · 2017-05-23 12:20:17Z

2

It looks to me like those are ndarrays of strings.

>>> numpy.array(['1', '2', '3']) * numpy.array(['1', '2', '3'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for *: 'numpy.ndarray' and 'numpy.ndarray'

You need to convert them to floatss or ints if you want to multiply them:

>>> numpy.array([1, 2, 3]) * numpy.array([1, 2, 3])
array([1, 4, 9])

One way to do that might be something like this. (But it depends on what you're passing to the function.)

Istack1 = np.array(map(float, Istack1))

Or, using a list comprehension:

Istack1 = np.array([float(i) for i in Istack1])

Or, stealing from HYRY (I forgot about the obvious approach):

Istack1 = np.array(Istack1, dtype='f8')

edited May 23, 2017 at 12:20

CommunityBot

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answered May 8, 2012 at 3:53

senderle

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1 Comment

T May Over a year ago

Of course! Thanks alot. The list comprehension method throws an error, but the map to float and HYRY's version works. I am passing a slice of a Tuple generated from appending csv file columns. I guess I could just do the float conversion before I pass it to the function.

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