conditional statement execution in numpy array with for loop

Question

X = data[['x_1','x_2']].as_matrix()
y = data['y'].as_matrix()

X_pos = np.array([[X[i]  for i in range(6)if y==1]])

y is a numpy array with some values of 0 and 1.

can somebody help me with the syntax ?

  X_pos = np.array([np.array([X[i]  for i in range(8)])[y[:8].astype('bool')]])
  X_neg = np.array([[np.logical_not(y)]])

Printing X_pos,

[[[ 1.          0.87142857  0.62458472]
  [ 1.         -0.02       -0.92358804]
  [ 1.          0.36285714 -0.31893688]
  [ 1.          0.88857143 -0.87043189]]]

When I print X_neg, I am getting only

[[[ True  True  True  True False False False False]]]

Instead I should get like this ,

[[ 1.         -0.80857143  0.8372093 ]
 [ 1.          0.35714286  0.85049834]
 [ 1.         -0.75142857 -0.73089701]
 [ 1.         -0.3         0.12624585]]

Why does it matter? The L just indicates a long integer, I'm not sure why you would be concerned about it. — miradulo
– miradulo, Commented Feb 17, 2017 at 21:30
Why, though? Like, what is your goal? Are you putting the shape in a string and using it somehow? Do you dislike the letter L? — miradulo
– miradulo, Commented Feb 17, 2017 at 21:57
nope...I have seen print the shape without the letter L...so I got confused whether I have to typecast — Kathiravan Natarajan
– Kathiravan Natarajan, Commented Feb 17, 2017 at 21:59

Yasin Yousif · Accepted Answer · 2017-02-20 01:48:56Z

1

assuming x and y are numpy arrays, your third line has the problem, you could rewrite it like that:

X_pos = np.array([np.array([X[i]  for i in range(6)])[y[:6].astype('bool')]])

for the fasle valuse (in y) use:

y_n = numpy.logical_not(y)
X_pos2 = np.array([np.array([X[i]  for i in range(6)])[y_n[:6]]])

here's what happen:

you take all the 6 elements of X
you apply a boolean mask of y elements for numpy array.
converting the whole result to numpy array (for some reason) as in your question..

edited Feb 20, 2017 at 1:48

answered Feb 18, 2017 at 1:46

Yasin Yousif

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5 Comments

Kathiravan Natarajan Over a year ago

the above statement is for true conditions of y right ? @Yasin Yousif ? I need put the false conditions in another numpy array. How can I do it ?

Yasin Yousif Over a year ago

it is mask of true and false ,..y , that the condition , but if u want the ommitted part , you can simply nigate y using numpy.logical_not(y)

Kathiravan Natarajan Over a year ago

I want to get the values of X whose y values are 0. # numpy.logical_not(y) from this I am getting true and false list.

Kathiravan Natarajan Over a year ago

Thanks @Yasin Yousif : Could you suggest me a link or material for learning typical numpy other than documentation ? Because doc couldn't help me in the above issue.

Yasin Yousif Over a year ago

here it is, just learn the basic orders in numpy,then at every problem use auto complete , or docs (with good ide ,ex:spyder), try googling your problem with keyword:"numpy", Franckly , I learned numpy from opencv-python docs as start ,then just from the numpy docs

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