title: How to read element by element an array inside an array in python
body: <p>I want to calculate the MSE of between two vectors, the original one and a prediction.
  X_train is a vector with all the original inputs and reconstructed32 are all the predictions, but I only want to calculate the MSE for the first element (X_train[0] and its prediction reconstructed32[0]), and I want do do it manually using some sort of function as the following:</p>
  <pre><code>mse=[]
  for coef, coef32 in zip(X_train[0], reconstructed32[0]):
      mse.append((coef-coef32)**2)
  print(&quot;MSE is&quot;, np.mean(mse))
  </code></pre>
  <p>But coef and coef32 do not access all the coefficients of the vector, instead they take the full vector and the for does only one iteration.
  This is how X_train[0] looks like:</p>
  <pre><code>array([[0.00000000e+00, 0.00000000e+00, 2.26577651e-02, 4.44901595e-03,
          0.00000000e+00, 0.00000000e+00, 0.00000000e+00, 0.00000000e+00,
          1.19896736e-02, 2.88007129e-03, 0.00000000e+00, 0.00000000e+00,
          1.89431056e-01, 0.00000000e+00, 3.64951454e-02, 0.00000000e+00,
          3.19024414e-01, 7.74396257e-03, 6.00360870e-01, 0.00000000e+00,
          6.25879224e-03, 6.58161461e-01, 8.55771124e-01, 0.00000000e+00,
          9.72116515e-02, 1.20666134e-03, 1.45429194e-01, 0.00000000e+00,
          8.25748563e-01, 6.86123502e-03, 5.37337780e-01, 0.00000000e+00,
          0.00000000e+00, 5.24137542e-03, 0.00000000e+00, 3.74730385e-04,
          0.00000000e+00, 1.18224040e-01, 8.56024176e-02, 0.00000000e+00,
          2.49160156e-02, 0.00000000e+00, 8.91805351e-01, 2.61418521e-03,
          0.00000000e+00, 1.73141190e-03, 0.00000000e+00, 4.95929737e-04,
          0.00000000e+00, 1.00000000e+00, 4.93207388e-02, 5.37037617e-03,
          3.81159922e-03, 2.94345170e-01, 4.77780886e-02, 0.00000000e+00,
          5.86739518e-02, 1.02838585e-02, 1.41941339e-01, 3.23100435e-03,
          0.00000000e+00, 1.34332031e-01, 2.35870923e-03, 0.00000000e+00,
          5.09367557e-03, 0.00000000e+00, 1.07753032e-03, 0.00000000e+00,
          0.00000000e+00, 0.00000000e+00, 3.47328931e-01, 0.00000000e+00,
          0.00000000e+00, 2.65773922e-01, 1.57823116e-02, 5.41949784e-03,
          7.56190493e-05, 1.40293926e-01, 5.02460590e-03, 6.51085284e-03,
          9.38402303e-03, 2.63461888e-01, 1.96186375e-04, 1.39610067e-01,
          0.00000000e+00, 2.39743218e-02, 3.54982950e-02, 6.54916763e-02,
          5.11557400e-01, 3.56561318e-03, 5.72423302e-02, 0.00000000e+00,
          1.21502653e-01, 2.71597654e-02, 2.47318600e-03, 6.85532205e-03,
          5.31266391e-01, 0.00000000e+00, 0.00000000e+00, 2.94529963e-02,
          0.00000000e+00, 3.75285745e-01, 3.31357837e-01, 1.18085509e-03,
          1.19613800e-02, 6.72158494e-05, 0.00000000e+00, 0.00000000e+00,
          0.00000000e+00, 7.86180317e-01, 0.00000000e+00, 0.00000000e+00,
          4.27392730e-03, 2.27557942e-02, 1.35929761e-02, 1.27607910e-02,
          0.00000000e+00, 2.63269083e-03, 1.48336608e-02, 0.00000000e+00,
          1.77292936e-02, 1.18409727e-04, 0.00000000e+00, 5.49420249e-03,
          0.00000000e+00, 1.70363311e-03, 1.75287843e-01, 4.07821295e-04]],
        dtype=float32)
  </code></pre>
  <p>As an example, if I try this simple code:</p>
  <pre><code>for coef in X_train[0]:
      print(&quot;coef is&quot;, coef)
  </code></pre>
  <p>I get this output:</p>
  <pre><code>coef is [0.00000000e+00 0.00000000e+00 2.26577651e-02 4.44901595e-03
   0.00000000e+00 0.00000000e+00 0.00000000e+00 0.00000000e+00
   1.19896736e-02 2.88007129e-03 0.00000000e+00 0.00000000e+00
   1.89431056e-01 0.00000000e+00 3.64951454e-02 0.00000000e+00
   3.19024414e-01 7.74396257e-03 6.00360870e-01 0.00000000e+00
   6.25879224e-03 6.58161461e-01 8.55771124e-01 0.00000000e+00
   9.72116515e-02 1.20666134e-03 1.45429194e-01 0.00000000e+00
   8.25748563e-01 6.86123502e-03 5.37337780e-01 0.00000000e+00
   0.00000000e+00 5.24137542e-03 0.00000000e+00 3.74730385e-04
   0.00000000e+00 1.18224040e-01 8.56024176e-02 0.00000000e+00
   2.49160156e-02 0.00000000e+00 8.91805351e-01 2.61418521e-03
   0.00000000e+00 1.73141190e-03 0.00000000e+00 4.95929737e-04
   0.00000000e+00 1.00000000e+00 4.93207388e-02 5.37037617e-03
   3.81159922e-03 2.94345170e-01 4.77780886e-02 0.00000000e+00
   5.86739518e-02 1.02838585e-02 1.41941339e-01 3.23100435e-03
   0.00000000e+00 1.34332031e-01 2.35870923e-03 0.00000000e+00
   5.09367557e-03 0.00000000e+00 1.07753032e-03 0.00000000e+00
   0.00000000e+00 0.00000000e+00 3.47328931e-01 0.00000000e+00
   0.00000000e+00 2.65773922e-01 1.57823116e-02 5.41949784e-03
   7.56190493e-05 1.40293926e-01 5.02460590e-03 6.51085284e-03
   9.38402303e-03 2.63461888e-01 1.96186375e-04 1.39610067e-01
   0.00000000e+00 2.39743218e-02 3.54982950e-02 6.54916763e-02
   5.11557400e-01 3.56561318e-03 5.72423302e-02 0.00000000e+00
   1.21502653e-01 2.71597654e-02 2.47318600e-03 6.85532205e-03
   5.31266391e-01 0.00000000e+00 0.00000000e+00 2.94529963e-02
   0.00000000e+00 3.75285745e-01 3.31357837e-01 1.18085509e-03
   1.19613800e-02 6.72158494e-05 0.00000000e+00 0.00000000e+00
   0.00000000e+00 7.86180317e-01 0.00000000e+00 0.00000000e+00
   4.27392730e-03 2.27557942e-02 1.35929761e-02 1.27607910e-02
   0.00000000e+00 2.63269083e-03 1.48336608e-02 0.00000000e+00
   1.77292936e-02 1.18409727e-04 0.00000000e+00 5.49420249e-03
   0.00000000e+00 1.70363311e-03 1.75287843e-01 4.07821295e-04]
  
  </code></pre>
  <p>And I would like to get &quot;coef is&quot; in front of every coefficient, not in front of the full vector. How can I solve this?</p>
  <p>Thanks!</p>