Unit-I Objects,Attributes,Similarity&Dissimilarity.ppt

Data science
UNIT-I
Data objects and Attribute types
Similarity and Dissimilarity
1

Types of Data Sets
• Record
• Relational records
• Data matrix, e.g., numerical matrix, crosstabs
• Document data: text documents: term-
frequency vector
• Transaction data
• Graph and network
• World Wide Web
• Social or information networks
• Molecular Structures
• Ordered
• Video data: sequence of images
• Temporal data: time-series
• Sequential Data: transaction sequences
• Genetic sequence data
• Spatial, image and multimedia:
• Spatial data: maps
• Image data:
• Video data:
Document 1
season
timeout
lost
wi
n
game
score
ball
pla
y
coach
team
Document 2
Document 3
3 0 5 0 2 6 0 2 0 2
0
0
7 0 2 1 0 0 3 0 0
1 0 0 1 2 2 0 3 0
TID Items
1 Bread, Coke, Milk
2 Beer, Bread
3 Beer, Coke, Diaper, Milk
4 Beer, Bread, Diaper, Milk
5 Coke, Diaper, Milk
2

Important characteristics of Structured data
• Dimensionality
• Curse of dimensionality
• Sparsity
• Only presence counts
• Resolution
• Patterns depend on the scale
• Distribution
• Centrality and dispersion
3
Data: 1. Structured
2. Unstructured
3. Semi structured
4. Quasi structured

Data Objects
• Data sets are made up of data objects.
• A data object represents an entity.
• Examples:
• sales database: customers, store items, sales
• medical database: patients, treatments
• university database: students, professors, courses
• Also called samples , examples, instances, data points,
objects, tuples.
• Data objects are described by attributes.
• Database rows -> data objects; columns ->attributes.
5

Attributes
• Attribute (or dimensions, features, variables): a data field, representing a
characteristic or feature of a data object.
• E.g., customer _ID, name, address
• Types:
• Nominal
• Binary
• Ordinal
• Continuous and Discontinues
• Numeric: quantitative
• Interval-scaled
• Ratio-scaled
6

8
Nominal Attributes-related to names

Similarity and Dissimilarity
Proximity: refers to a similarity or dissimilarity
12
Similarity

Similarity and Dissimilarity Applications:
• Web search
• Computer vision:
• Image Processing
• Natural language processing
• Clustering outliers
13

Similarity / Proximity Measures
14
• Nominal attributes
• Binary attributes
• Ordinal attributes
• Numeric attributes 1. Scaled 2. Ratio
• Mixed attributes

Data Matrix and Dissimilarity Matrix
15
Data Matrix

Proximity Measure for Nominal Attributes
16

Example: Finding Similarity matrix for Nominal attribute
19

Example : find dissimilarity of given data
20

Proximity Measure for Binary Attributes
21

• A contingency table for binary data
• Distance measure for symmetric binary
variables:
• Distance measure for asymmetric binary
variables:
• Jaccard coefficient (similarity measure
for asymmetric binary variables):
22
 Note: Jaccard coefficient is the same as “coherence”:
Object i
Object j

Proximity Measure for Binary Attributes: Example
23

24

• Example
• Gender is a symmetric attribute
• The remaining attributes are asymmetric binary
• Let the values Y and P be 1, and the value N 0
25
Name Gender Fever Cough Test-1 Test-2 Test-3 Test-4
Jack M Y N P N N N
Mary F Y N P N P N
Jim M Y P N N N N
75
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mary
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d
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jack
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d
Proximity Measure for Binary Attributes: Example: Find Dissimilarity
matrix

Proximity Measure for Numeric Attributes: Standardizing Numeric Data
• Z-score:
• X: raw score to be standardized, μ: mean of the population, σ: standard
deviation
• the distance between the raw score and the population mean in units of
the standard deviation
• negative when the raw score is below the mean, “+” when above
• An alternative way: Calculate the mean absolute deviation
where
• standardized measure (z-score):
• Using mean absolute deviation is more robust than using standard deviation



 x
z
26
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Data Matrix and Dissimilarity Matrix
27
point attribute1 attribute2
x1 1 2
x2 3 5
x3 2 0
x4 4 5
Dissimilarity Matrix
(with Euclidean Distance)
x1 x2 x3 x4
x1 0
x2 3.61 0
x3 5.1 5.1 0
x4 4.24 1 5.39 0
Data Matrix

Distance on Numeric Data: Minkowski Distance
• Minkowski distance: A popular distance measure
where i = (xi1, xi2, …, xip) and j = (xj1, xj2, …, xjp) are two p-
dimensional data objects, and h is the order (the distance
so defined is also called L-h norm)
• Properties
• d(i, j) > 0 if i ≠ j, and d(i, i) = 0 (Positive definiteness)
• d(i, j) = d(j, i) (Symmetry)
• d(i, j)  d(i, k) + d(k, j) (Triangle Inequality)
• A distance that satisfies these properties is a metric
28

Special Cases of Minkowski Distance
• h = 1: Manhattan (city block, L1 norm) distance
• E.g., the Hamming distance: the number of bits that are different
between two binary vectors
• h = 2: (L2 norm) Euclidean distance
• h  . “supremum” (Lmax norm, L norm) distance.
• This is the maximum difference between any component
(attribute) of the vectors
|
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p j
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29
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Example: Minkowski Distance
30
Dissimilarity Matrices
point attribute 1 attribute 2
x1 1 2
x2 3 5
x3 2 0
x4 4 5
L x1 x2 x3 x4
x1 0
x2 5 0
x3 3 6 0
x4 6 1 7 0
L2 x1 x2 x3 x4
x1 0
x2 3.61 0
x3 2.24 5.1 0
x4 4.24 1 5.39 0
L x1 x2 x3 x4
x1 0
x2 3 0
x3 2 5 0
x4 3 1 5 0
Manhattan (L1)
Euclidean (L2)
Supremum

Example : Numeric attribute: Find the distances
31

Example: Ratio-Scaled Attributes: Find Dissimilarity matrix
33

Example: find Dissimilarity of given Numeric
data
34

Proximity measure for Ordinal attributes
• An ordinal variable can be discrete or continuous
• Order is important, e.g., rank
• Can be treated like interval-scaled
• replace xif by their rank
• map the range of each variable onto [0, 1] by replacing i-th object in
the f-th variable by
• compute the dissimilarity using methods for interval-scaled variables
35
1
1



f
if
if M
r
z
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,...,
1
{ f
if
M
r 

Example: Ordinal Attributes
36

Example: Ordinal Attributes
37

Example: Find Dissimilarity matrix of given
ordinal attribute
38

Proximity measures of Mixed Attributes
• A database may contain all attribute types
• Nominal, symmetric binary, asymmetric binary, numeric,
ordinal
• One may use a weighted formula to combine their effects
• f is binary or nominal:
dij
(f) = 0 if xif = xjf , or dij
(f) = 1 otherwise
• f is numeric: use the normalized distance
• f is ordinal
• Compute ranks rif and
• Treat zif as interval-scaled
)
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1
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39

40
Example: Find Dissimilarity of Mixed Attributes

41

42

Cosine Similarity
• A document can be represented by thousands of attributes, each recording the
frequency of a particular word (such as keywords) or phrase in the document.
• Other vector objects: gene features in micro-arrays, …
• Applications: information retrieval, biologic taxonomy, gene feature mapping, ...
• Cosine measure: If d1 and d2 are two vectors (e.g., term-frequency vectors), then
cos(d1, d2) = (d1  d2) /||d1|| ||d2|| ,
where  indicates vector dot product, ||d||: the length of vector d
47

Example: Find similarity of documents
• cos(d1, d2) = (d1  d2) /||d1|| ||d2|| ,
where  indicates vector dot product, ||d|: the length of vector d
• Ex: Find the similarity between documents 1 and 2.
d1 = (5, 0, 3, 0, 2, 0, 0, 2, 0, 0)
d2 = (3, 0, 2, 0, 1, 1, 0, 1, 0, 1)
d1d2 = 5*3+0*0+3*2+0*0+2*1+0*1+0*1+2*1+0*0+0*1 = 25
||d1||= (5*5+0*0+3*3+0*0+2*2+0*0+0*0+2*2+0*0+0*0)0.5=(42)0.5 = 6.481
||d2||= (3*3+0*0+2*2+0*0+1*1+1*1+0*0+1*1+0*0+1*1)0.5=(17)0.5 = 4.12
cos(d1, d2 ) = 0.94
48

Unit-I Objects,Attributes,Similarity&Dissimilarity.ppt

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Unit-I Objects,Attributes,Similarity&Dissimilarity.ppt