Efficient ways to iterate the dataset
It seems that selecting a subset of colums directly from the dataset, i.e., dataset["column"], is slow. I was wrong, ```dataset["column"]``` is fast.
For a large dataset that does not fits the memory, how can I select only a subset of features from each example?

If I iterate over the dataset and then select the subset of features one by one, the resulted memory usage will be huge. Any ways to solve this?

Thanks