A missing value is an absent or unrecorded value for an attribute in a data record. In machine-learning data, missing values make examples harder to compare and can cause problems for algorithms. section 8.8
Table 8.2 The diamond dataset with missing and inconsistent data
|
Carat |
Cut |
Color |
Clarity |
Depth |
Table |
Price |
X |
Y |
Z |
|
| 1 |
0.30 |
Good |
J |
SI1 |
64.0 |
55 |
339 |
4.25 |
4.28 |
2.73 |
| 2 |
0.41 |
Ideal |
I |
si1 |
61.7 |
55 |
561 |
4.77 |
4.80 |
2.95 |
| 3 |
0.75 |
Very good |
D |
SI1 |
63.2 |
56 |
2,760 |
5.80 |
5.75 |
3.65 |
| 4 |
0.91 |
– |
H |
SI2 |
– |
60 |
2,763 |
6.03 |
5.99 |
3.95 |
| 5 |
1.20 |
Fair |
F |
I1 |
64.6 |
56 |
2,809 |
6.73 |
6.66 |
4.33 |
| 6 |
1.21 |
Good |
E |
I1 |
57.2 |
62 |
3,144 |
7.01 |
6.96 |
3.99 |
| 7 |
1.31 |
Premium |
J |
SI2 |
59.7 |
59 |
3,697 |
7.06 |
7.01 |
4.20 |
| 8 |
1.50 |
Premium |
H |
I1 |
62.9 |
60 |
4,022 |
7.31 |
7.22 |
4.57 |
| 9 |
1.74 |
Very good |
H |
i1 |
63.2 |
55 |
4,677 |
7.62 |
7.59 |
4.80 |
| 10 |
1.83 |
fair |
J |
I1 |
70.0 |
58 |
5,083 |
7.34 |
7.28 |
5.12 |
| 11 |
1.96 |
Fair |
I |
I1 |
66.8 |
55 |
6,147 |
7.62 |
7.60 |
5.08 |
| 12 |
– |
Premium |
H |
i1 |
62.2 |
– |
6,535 |
8.31 |
– |
5.16 |
The diamond dataset shows missing Cut and Depth values in one example and missing Carat, Table, and Y values in another. section 8.8
Common ways to handle missing values include:
- Remove examples containing missing features. This avoids making assumptions, but may discard records important to the task. section 8.8
- Replace numeric missing values with a feature’s mean or median. The mean is efficient but ignores feature relationships and does not suit categorical features. section 8.8
- Estimate a missing value from related features when a meaningful relationship exists, such as using diamond dimensions for a missing measurement. section 8.13 section 8.9
A diamond record with missing data
Suppose a record lacks Cut and Depth. Removing the record preserves observed values but reduces the dataset. Replacing numeric values with a mean or median may preserve the record, while the categorical Cut value needs another treatment or estimation. section 8.8 section 8.9


































