['0', '0', '0']
['1', '1', '1']
['?', '?', '1']
['~', '~', '~']
['?', '?', '?']
['?', '?', '?']
['?', '?', '?']
['~', '~', '~']
['X', 'X', 'X']
['UNK', 'UNK', 'UNK']
['UNAVAILABLE', 'UNAVAILABLE', 'UNAVAILABLE']
Default saving

a	b	c
0 1 UNAVAILABLE UNK X	0 1 UNAVAILABLE UNK X	0 1 UNAVAILABLE UNK X
		
0	0	0
1	1	1
?	?	1
~	~	~
?	?	?
?	?	?
?	?	?
~	~	~
X	X	X
UNK	UNK	UNK
UNAVAILABLE	UNAVAILABLE	UNAVAILABLE

Saving with all undefined as NA

a	b	c
0 1 UNAVAILABLE UNK X	0 1 UNAVAILABLE UNK X	0 1 UNAVAILABLE UNK X
		
0	0	0
1	1	1
?	?	1
~	~	~
?	?	?
?	?	?
?	?	?
~	~	~
X	X	X
UNK	UNK	UNK
UNAVAILABLE	UNAVAILABLE	UNAVAILABLE

Saving with all undefined as NA

a	b	c
0 1 UNAVAILABLE UNK X	0 1 UNAVAILABLE UNK X	0 1 UNAVAILABLE UNK X
		
0	0	0
1	1	1
?	?	1
~	~	~
?	?	?
?	?	?
?	?	?
~	~	~
X	X	X
UNK	UNK	UNK
UNAVAILABLE	UNAVAILABLE	UNAVAILABLE

