How to sort a Matrix

In below code we have a population 'P' of size 'NP' which has two fields 'Position' and 'Cost'. I need to sort the entire population 'P' with respect to field 'Cost' and select top p elements (say p = 4).

clc; clear all;

varMin   = -5;           
varMax   =  5; 
D        =  3;    % Dimension
VarSize  = [1 D]; % Decision Variables Matrix Size
NP       = 10;    % Population size
empty_individual.Position   = []; % Field 1
empty_individual.Cost       = []; % Field 2

P  = repmat(empty_individual, NP, 1); % Population

CostFunction = @(x) sphere(x);

%%Generating random population

for i = 1:NP
    P(i).Position = unifrnd(varMin, varMax, VarSize);
    P(i).Cost       = CostFunction(P(i).Position);
end

% add Code here

sphere.m

function ret = sphere(x)
    ret = sum(x.^2);
end

Answer 1

[Andrei Bobrov]

p = 4;

data = [P.Cost]';
[~,ii] = sort(data);
out = P(ii(1:p));