根據第二個矩陣中給出的順序對矩陣進行排序（MATLAB）

Question

我有一個已排序的bigmatrix。但是，我需要按照另一個矩陣中的ID順序重新排序（col. 1 here for both matrices）。我怎樣才能做到這一點使用矢量化？例如：

bigmat = [ ... 
      1 10 ; 
      1 30 ; 
      1 40 ; 
      2 1 ; 
      2 11 ; 
      3 58 ; 
      4 2 ; 
      4 5 ] ; 

ordermat = [ 2 ; 1 ; 4 ; 3 ; 6] ;  % Integer IDs 

finalans = [ ... 
      2 1 ; 
      2 11 ; 
      1 10 ; 
      1 30 ; 
      1 40 ; 
      4 2 ; 
      4 5 ; 
      3 58 ; ] ; 

這可能是所有的一些的ID（此處整數）在ordermat可能不會出現在bigmat。如上所示，可以忽略它們，其編號爲id = 6。謝謝！

Answer 1

%# Input values: 
bigmat = [1 10; 1 30; 1 40; 2 1; 2 11; 3 58; 4 2; 4 5]; 
ordermat = [ 2 ; 1 ; 4 ; 3 ; 6] ; 

%# Make a look-up table that tells us the relative order for each order id 
sortmat(ordermat) = 1:length(ordermat); 

%# Extract the order ID's from the big matrix 
keys = bigmat(:,1); 

%# Get the new ordering 
new_key = sortmat(keys); 

%# Sort the new ordering, remembering the permutation necessary 
[~, permutation] = sort(new_key); 

%# Apply the permutation to the big matrix 
finalans = bigmat(permutation, :); 

Answer 2

這裏是我的解決方案：

ordermat = [2; 1; 4; 3; 6]; 
bigmat = [ 
    1 10 
    1 30 
    1 40 
    2 1 
    2 11 
    3 58 
    4 2 
    4 5 
]; 
%#bigmat = sortrows(bigmat,1); 

%# keep valid IDs, 
ord = ordermat(ismember(ordermat,bigmat(:,1))); 
ord = grp2idx(ord); 

%# starting/ending locations of the different IDs in bigmat 
startInd = find(diff([0;bigmat(:,1)])); 
endInd = [startInd(2:end)-1; size(bigmat,1)]; 

%# generate startInd(i):endInd(i) intervals 
ind = arrayfun(@colon, startInd, endInd, 'UniformOutput',false); 

%# order then combine the intervals of indices 
ind = [ind{ord}]; 

%# get final sorted result 
finalans = bigmat(ind,:); 

我確信它可以處理不同的情況，如：

• ordermat包含bigmat未發現標識：不是bigmat所有ID都代表ordermat = [2;1;4;3;6]
• 在ordermat中：ordermat = [2;1]
• ID不連續和/或無法啓動在1：ordermat=ordermat+10; bigmat=bigmat+10;

Answer 3

我會根據唯一標識符拆分bigmat成塊，然後重新排列塊，像這樣：

%# this assumes bigmat is sorted, btw 
%# i.e. that the different ids are grouped together 

%# find unique ids 
dd = [true;diff(bigmat(:,1))~=0]; 

uniqueIDs = bigmat(dd,1); 

%# reorder uniqueIDs 
[~,newOrder] = ismember(uniqueIDs,ordermat); 

%# if there are uniqueIDs that are not in ordermat 
%# we'd need to remove those. I assume this won't 
%# be the case 

%# chop up bigmat 
numUniqueIds = diff([find(dd);length(dd)+1]); 
bigChunks = mat2cell(bigmat,numUniqueIds,size(bigmat,2)); 

%# reorder chunks 
finalans = cat(1,bigChunks{newOrder});