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How to convert Non Sparse Data to Sparse Data In Weka

Sparse ARFF files

Sparse ARFF files are very similar to ARFF files, but data with value 0 are not being explicitly represented.

Example with 0 input
@data
0, X, 0, Y, "class A"
0, 0, W, 0, "class B"

Implementation of sparse arff file
Format:"index space value" where index is the
attribute index (starting from 0).

Remark: non-zero attributes are explicitly identified by attribute number and their value stated.
Example
@data
1 X, 3 Y, 4 "class A"
2 W, 4 "class B"
Note: that the omitted values in a sparse instance are 0, they are not "missing" values! If a value is unknown, you must explicitly represent it with a question mark ?.