wkeep

Keep part of vector or matrix

Syntax

Y = wkeep(X,L,opt)

Y = wkeep(X,L,first)

Y = wkeep(X,S)

Y = wkeep(X,S,[firstr,firstc])

Description

Y = wkeep(X,L,opt) extracts the vector Y from the vector X. The length of Y is L.

If opt is 'c', 'l', or 'r', Y is the central, left, or right part, respectively, of X.

The syntax Y = wkeep(X,L) is equivalent to Y = wkeep(X,L,'c').

Y = wkeep(X,L,first) extracts the vector X(first:first+L-1).

Y = wkeep(X,S) extracts the central part of the matrix X. The size of Y is S.

Y = wkeep(X,S,[firstr,firstc]) extracts the submatrix of the matrix X, of size S and starting from X(firstr,firstc).

Examples

Extract from Vector and Matrix

Create a vector.

x = 1:10;

Extract a vector of length 6 from the central part of x. Confirm both possible syntaxes return the same vector.

y = wkeep(x,6,'c')

y = 1×6

     3     4     5     6     7     8

y = wkeep(x,6)

y = 1×6

     3     4     5     6     7     8

Extract a vector of length 7 from the central part of x.

y = wkeep(x,7,'c')

y = 1×7

     2     3     4     5     6     7     8

Extract two vectors of length 6, one from the left part of x, and the other from the right part of x.

y = wkeep(x,6,'l')

y = 1×6

     1     2     3     4     5     6

y = wkeep(x,6,'r')

y = 1×6

     5     6     7     8     9    10

Create a 5-by-5 matrix.

x = magic(5)

x = 5×5

    17    24     1     8    15
    23     5     7    14    16
     4     6    13    20    22
    10    12    19    21     3
    11    18    25     2     9

Extract from the center of x a 3-by-2 matrix.

y = wkeep(x,[3 2])

y = 3×2

     5     7
     6    13
    12    19

Extract from x the 2-by-4 submatrix starting at x(3,1).

y = wkeep(x,[2 4],[3 1])

y = 2×4

     4     6    13    20
    10    12    19    21

Input Arguments

X — Input

vector | matrix

Input, specified as a vector or matrix.

Data Types: single | double

L — Length of vector to extract

integer | Inf

Length of vector to extract from the input vector X, specified as an integer or Inf. If L is specified as Inf, wkeep returns the input vector X.

Data Types: single | double

opt — Location of extraction

'c' | 'l' | 'r'

Location of extraction from the input vector X, specified as:

• 'c' — central part of the vector

• 'l' — left part of the vector

• 'r' — right part of the vector

Example: wkeep(1:10,4,'r') returns the extraction [7 8 9 10].

first — Starting index

positive integer

Starting index of the input vector X, specified as a positive integer. The first element in the extraction is X(first).

Data Types: single | double

S — Dimensions of submatrix

two-element vector

Dimensions of submatrix to extract from the input matrix X, specified as a two-element vector. Each element of S is a positive integer or Inf.

Example: If X is a 27-by-5 matrix, wkeep(X,[Inf 3]) extracts the 27-by-3 submatrix from the central part of X.

Data Types: single | double

firstr,firstc — Starting row, column indices

two positive integers

Starting row, column indices of the input matrix X, specified as two positive integers. The value of the extraction Y(1,1) is X(firstr,firstc).

Example: wkeep(X,[3 2],[1 4]) extracts a 3-by-2 submatrix from the matrix X starting from X(1,4).

Data Types: single | double

Extended Capabilities

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The wkeep function fully supports GPU arrays. To run the function on a GPU, specify the input data as a gpuArray (Parallel Computing Toolbox). For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced before R2006a