MATLAB Function Reference

sortrows - Sort rows in ascending order

Syntax

B = sortrows(A)
B = sortrows(A,column)
[B,index] = sortrows(A,...)

Description

B = sortrows(A) sorts the rows of A in ascending order. Argument A must be either a matrix or a column vector.

For strings, this is the familiar dictionary sort. When A is complex, the elements are sorted by magnitude, and, where magnitudes are equal, further sorted by phase angle on the interval .

B = sortrows(A,column) sorts the matrix based on the columns specified in the vector column. If an element of column is positive, the MATLAB^® software sorts the corresponding column of matrix A in ascending order; if an element of column is negative, MATLAB sorts the corresponding column in descending order. For example, sortrows(A,[2 -3]) sorts the rows of A first in ascending order for the second column, and then by descending order for the third column.

[B,index] = sortrows(A,...) also returns an index vector index.

If A is a column vector, then B = A(index). If A is an m-by-n matrix, then B = A(index,:).

Examples

Start with a mostly random matrix, A:

rand('state',0)
A = floor(rand(6,7) * 100);
A(1:4,1)=95;  A(5:6,1)=76;  A(2:4,2)=7;  A(3,3)=73
A =
    95    45    92    41    13     1    84
    95     7    73    89    20    74    52
    95     7    73     5    19    44    20
    95     7    40    35    60    93    67
    76    61    93    81    27    46    83
    76    79    91     0    19    41     1

When called with only a single input argument, sortrows bases the sort on the first column of the matrix. For any rows that have equal elements in a particular column, (e.g., A(1:4,1) for this matrix), sorting is based on the column immediately to the right, (A(1:4,2) in this case):

sortrows(A)
ans =
    76    61    93    81    27    46    83
    76    79    91     0    19    41     1
    95     7    40    35    60    93    67
    95     7    73     5    19    44    20
    95     7    73    89    20    74    52
    95    45    92    41    13     1    84

When called with two input arguments, sortrows bases the sort entirely on the column specified in the second argument. Rows that have equal elements in this column are sorted; rows with equal elements in other columns are left in their original order:

sortrows(A,1)
ans =
    76    61    93    81    27    46    83
    76    79    91     0    19    41     1
    95    45    92    41    13     1    84
    95     7    73    89    20    74    52
    95     7    73     5    19    44    20
    95     7    40    35    60    93    67

This example specifies two columns to sort by: columns 1 and 7. This tells sortrows to sort by column 1 first, and then for any rows with equal values in column 1, to sort by column 7:

sortrows(A,[1 7])
ans =
    76    79    91     0    19    41     1
    76    61    93    81    27    46    83
    95     7    73     5    19    44    20
    95     7    73    89    20    74    52
    95     7    40    35    60    93    67
    95    45    92    41    13     1    84

Sort the matrix using the values in column 4 this time and in reverse order:

sortrows(A, -4)
ans =
    95     7    73    89    20    74    52
    76    61    93    81    27    46    83
    95    45    92    41    13     1    84
    95     7    40    35    60    93    67
    95     7    73     5    19    44    20
    76    79    91     0    19    41     1

See Also

issorted, sort

sort

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