'Leave-P-Out cross validation iterator:
Provides train/test indexes to split data in train test sets
Parameters
n: int
Total number of elements
p: int
Size test sets
Examples
>>> from scikits.learn import cross_val
>>> X = [[1, 2], [3, 4], [5, 6], [7, 8]]
>>> y = [1, 2, 3, 4]
>>> lpo = cross_val.LeavePOut(4, 2)
>>> for train_index, test_index in lpo:
...    print "TRAIN:", train_index, "TEST:", test_index
...    X_train, X_test, y_train, y_test = cross_val.split(train_index, test_index, X, y)
TRAIN: [False False  True  True] TEST: [ True  True False False]
TRAIN: [False  True False  True] TEST: [ True False  True False]
TRAIN: [False  True  True False] TEST: [ True False False  True]
TRAIN: [ True False False  True] TEST: [False  True  True False]
TRAIN: [ True False  True False] TEST: [False  True False  True]
TRAIN: [ True  True False False] TEST: [False False  True  True]'

def __init__(self, n, p):

    self.n = n
    self.p = p
