a=[1 2;1 4;2 3;2 5;3 4;3 7;3 1];
%% 方法1
index =unique(a(:,1));
JG=[];
for i =1:length(index)
JG=[JG;[index(i),mean(a(a(:,1)==index(i),2))]];
end
%% 方法2利用表的groupsummary 组汇总计算
T=array2table(a, 'VariableNames',{'a1','a2'});
G = groupsummary(T,'a1','mean' );
temp=table2array(G);
out=temp(:,[1,3]);