Lab 1, get_batch function

In this function the length of the vectorized_songs is calculated as 
```
n = vectorized_songs.shape[0] - 1
```
why is there a minus 1 there

``` vectorized_songs.shape``` 
comes out to be 
```(200679,)```

shouldn't it be just 

```
n = vectorized_songs.shape[0] 
```
? 