title: What does matrix[x] for different x indicate?
body: <p>While using the MNIST datasetfrom kaggle,i have noticed that all the tutorials use mnist[x] for different values of x to retrieve different pictures.</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  import matplotlib.pyplot as plt
  
  mnist=pd.read_csv(r"(dir of dataset)").values
  img=mnist[1]
  img.shape=(28,28)
  plt.imshow(img)
  plt.show()
  </code></pre>
  
  <p>My doubt is what <code>mnist[1]</code> retrieves,also i have noticed that <code>mnist[-1]</code> also works,so that is why i am confused.</p>