Closed topepo closed 7 years ago
Hi @topepo ,
Let's take https://wush978.github.io/FeatureHashing/#36 as an example:
As you can see, if the data have only one instance (one row), then the hashed feature will become 0x64
, 0x9b
and 0x36
. Therefore, there are 2^4 - 3
columns will be zero.
That is to say, the feature hashing might not map real features to all hashed feature. It depends on the data, hash space and the hashing algorithm.
Thanks!
I'm trying to understand why there are some hash features that have no keys mapped to them.
Here's an example where the number of features is significantly smaller than the number of original values but there are a few thousand features that are zero across all rows.
Thanks