how to apply different operators on two arrays with differents in python

Question

I have two arrays, each of them is composed by a pair of two integer (int1,int2). I want to compute a sum only on the first values of the pair of each array, and i want to apply a multiplication(for instance) on the second values. Clearly, if i write this code:

tab1=np.array([(1,2),(1,5),(0,6)])
tab2=np.array([(0,7),(1,4),(0,2)])
tab3=tab1+tab2
tab4=tab1*tb2

the result of tab3 will be tab3=array([[1, 9],[2, 9],[0, 8]])

The sum was applied also in the second part. but i want to obtain (1+0),(1+1),(0+0), thus: tab3=array([1,2,0])

Is it possible to have this result without do a loop on the arrays?

DSM · Accepted Answer · 2013-01-11 18:02:51Z

1

You can index to get the appropriate elements:

>>> tab1 = np.array([(1,2),(1,5),(0,6)])
>>> tab2 = np.array([(0,7),(1,4),(0,2)])
>>> tab1
array([[1, 2],
       [1, 5],
       [0, 6]])
>>> tab1[:,0]
array([1, 1, 0])
>>> tab1[:,1]
array([2, 5, 6])

and thus

>>> tab3 = tab1[:,0] + tab2[:,0]
>>> tab4 = tab1[:,1] * tab2[:,1]
>>> tab3
array([1, 2, 0])
>>> tab4
array([14, 20, 12])

answered Jan 11, 2013 at 18:02

DSM

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1 Comment

KKc Over a year ago

yes, it's the same procedure in Matlab for instance!!i had forgotten. thanks

LtWorf · Accepted Answer · 2013-01-11 18:22:02Z

0

#Calculates the adding and the multiplication
t=map((lambda x,y:(x[0]+y[0],x[1]*y[1])) , tab1,tab2)
#Splits the result
tab3,tab4 = zip(*t)

It must be noted that when using map, the loop is implicit but still occurs as internal magic.

answered Jan 11, 2013 at 18:22

LtWorf

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