Libsvm python error

Question

I'm trying to figure out what is the proper format of a python list to be given as input to a svm_problem function in python. I got the following program from the web, stackoverflow.

I have the following:

from svm import *
x=[ [1,0,1],[-1,0,-1],[1,0,0]]
#x=[ [1,0,1],[-1,0,-1]]
prob = svm_problem( [1,-1],x  )
param = svm_parameter(kernel_type = LINEAR, C = 10)
m = svm_model(prob, param)
print m.predict([ 1,1, 1])

It raises an assertion error, says assert failed: assert len(x)==len(y).

But if x=[ [1,0,1],[-1,0,-1]], the program works perfectly. Am I not supposed to give a train-data problem of length more than 2?

Also I don't understand what in x=[[1,0,1],[-1,0,-1]] is a label and what is the data?

Any help is highly appreciated.

carl · Accepted Answer · 2011-04-11 21:13:49Z

2

svm_problem() takes two parameters: the first parameter of a vector of labels, and the second is a matrix of features. You get this assertion error because you are only specifying 2 labels, [1, -1], as the first parameter in your call to svm_problem.

Example:

y = [1,-1,1,1]
x = [[1,0,1], [-1,0,-1], [1,2,3], [4,5,6]]
prob = svm_problem(y, x)

answered Apr 11, 2011 at 21:13

carl

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1 Comment

garak Over a year ago

I just figured that out. THank you very much

highBandWidth · Accepted Answer · 2011-04-11 21:16:09Z

0

If you give 3 examples, you need to give the classes for the three inputs as well, so you need to do

prob = svm_problem( [1,1,-1],x  )

or something similar.

answered Apr 11, 2011 at 21:16

highBandWidth

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