Record writer for SVMLight format, which can generally
be described as
LABEL INDEX:VALUE INDEX:VALUE ...
SVMLight format is well-suited to sparse data (e.g.,
bag-of-words) because it omits all features with value
We support an "extended" version that allows for multiple
targets (or labels) separated by a comma, as follows:
LABEL1,LABEL2,... INDEX:VALUE INDEX:VALUE ...
This can be used to represent either multitask problems or
multilabel problems with sparse binary labels (controlled
via the "MULTILABEL" configuration option).
Like scikit-learn, we support both zero-based and one-based indexing.
Further details on the format can be found at