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Vectors are created using the vector() function and matrices with the matrix() function. Their elements are read or set using the [] operator :
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#
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Allocate
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a
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vector
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of
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5
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elements
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v
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=
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vector(5)
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#
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Initialise
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their
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value
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for
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i
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=
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1
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to
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5
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do
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v[i]
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=
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i
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end
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for
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Vector literals can be written using the | character :
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v
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=
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|3,6,7,9,10|
How operators and functions work on vectors
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X[i] = ith value of vector X:
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#
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copies
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element
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2
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of
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vector
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X
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into
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Y
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Y
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=
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X[2]
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More sophisticated usage of [] allows you to extract or refer to a range of values.
x[i,j] = all values of vector X from the ith to the jth :
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#
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copies
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values
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3,
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4,
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5,
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6,
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7
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and
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8
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of
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X
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into
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Y
...
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Y
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=
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X[3,8]
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X[i,j,k] = every kth value of vector X, from the ith to the jth :
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#
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copies
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values
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1,
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5,
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9,
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13,
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17
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of
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X
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into
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Y
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Y
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=
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X[1,20,4]
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An additional fourth parameter specifies how many elements to extract from the current step :
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#
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copies
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values
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1,2,
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5,6,
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9,10,
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13,14,
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17,18
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of
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X
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into
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Y
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Y
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=
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X[1,20,4,2]
If a vector is holding data representing a rectangular structure, this form could be used to extract a 'sub-area'.
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Vectors can contain missing values. These can be assigned or tested for using the global variable vector_missing_value. Operations between vectors will bypass missing values. For example, if we represent a missing value with an 'x', then the result of
|1,2,3,x,5|
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+
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|2,2,2,2,x|
will be
|3,4,5,x,x|
See the descriptions for particular functions and operators for specific details. The bitmap() function can be used to translate between missing values and 'real' values. When a vector is printed with the print() function, missing values are represented by an 'x'.
When a vector is generated from a fieldset, e.g.
a
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=
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values(fieldset)
missing values from the field are automatically translated into missing values in the vector. The same is true when obtaining a vector of values from a geopoints variable. Missing values in vectors are also translated correctly when inserted into fieldsets and geopoints.