How to use NDArray like NumPy?

ND4J
1

I’m new to using DL4J and I’m trying to figure out how to use NDArray
What I’m trying to do is similar to the NumPy python np.array

Basically what I’m trying to do is add a dataframe of one column into the array.

For ex. if I have a dataframe like:

 Height
    t
    t
    t
    t
    s
    s
    s

Using NumPy I could do:

heightDataframe = ...
heightArray = np.array(heightDataframe)

and I get back an array like:

[['t'] 
['t']
['t']
['t']
['s']
['s']
['s']]

So I’m wondering how I could do something similar in ND4J?
I tried reading through the docs but I was a bit confused about how to get it started.

Any ideas would be great!
Thanks so much!

2

@yjay nd4j itself is just a “numpy”. In order to use it with a specific input pipeline, you normally use datavec with it.

We have examples of that here for csv data:

Nd4j can also ready numpy arrays directly. If you want to use python to do your ETL then just save numpy arrays we load that can work as well:

Unfortunately, we don’t have as much magic around auto data type conversion and do not support objects as input types. We do allow strings though. If you can tell me more specifically what you’re trying to do I can make a better recommendation.

1 Like
3

Thanks so much for this useful information!

Basically what I’m trying to do is make an array that can be used for data science predictions. More specifically at the moment I’m looking to use if for k-nearest neighbour. In knn.fit, I want to use a flattened array containing numpy.array for the values in knn.fit.

I also want to be able to use if later on for things like numpy.maximum and minimum.

4

@yjay then for columnar data, we typically use csv record readers and datavec. Like I mentioned, if you prefer python and pandas you can save your dataset as numpy arrays and we can directly load them.
For max and min you’ll want: