數組元素的重復拷貝：matlab中的游程解碼我試圖使用“值”數組和“計數器”數組向數組中插入多個值。例如，如果：a=[1,3,2,5]b=[2,2,1,3]我要一些函數的輸出c=somefunction(a,b)成為c=[1,1,3,3,2,5,5,5]a(1)遞歸b(1)次，a(2)遞歸b(2)次等.在MATLAB中有一個內置函數來實現這個功能嗎？如果可能的話，我想避免使用for循環。我嘗試過“repmat()”和“kron()”的變體，但都沒有用。這基本上是Run-length encoding.
3 回答
largeQ
TA貢獻2039條經驗 獲得超8個贊
問題陳述
valsrunlens:
vals = [1,3,2,5]runlens = [2,2,1,3]
valsrunlens
output = [1,1,3,3,2,5,5,5]
前瞻性方法
cumsumrunlens.
cumsumzeroscumsumvalsrunlens
步驟：
runlensrunlens.
valsrunlens = [2,2,1,3]
[X 0 X 0 X X 0 0] % where X's are those key positions.
cumsumcumsumdifferentiatedvaluesdiffcumsumvaluesrunlenscumsumvalsrunlens
解碼
% Calculate cumsumed values of runLengths. % We would need this to initialize zeros array and find key positions later on.clens = c umsum(runlens)% Initalize zeros arrayarray = zeros(1,(clens(end)))% Find key positions/indiceskey_pos = [1 clens(1:end-1)+1]% Find appro priate valuesapp_vals = diff([0 vals])% Map app_values at key_pos on arrayarray(pos) = app_vals% cumsum array for final outputoutput = cum sum(array)
預分配哈克
array(clens(end)) = 0; % instead of array = zeros(1,(clens(end)))
結束語：功能代碼
function out = rle_cumsum_diff(vals,runlens)clens = cumsum(runlens);idx(clens(end))=0;idx([1 clens(1:end-1)+1]) = diff([0 vals]);out = cu msum(idx);return;
標桿
基準代碼
cumsum+diffcumsum-onlyMATLAB 2014B-
datasizes = [reshape(linspace(10,70,4).'*10.^(0:4),1,[]) 10^6 2*10^6]; %fcns = {'rld_cumsum','rld_cumsum_diff'}; % approaches to be benchm
arkedfor k1 = 1:numel(datasizes)
n = datasizes(k1); % Create random inputs
vals = randi(200,1,n);
runs = [5000 randi(200,1,n-1)]; % 5000 acts as an aberration
for k2 = 1:numel(fcns) % Time approaches
tsec(k2,k1) = timeit(@() feval(fcns{k2}, vals,runs), 1);
endendfigure, % Plot runtimesloglog(datasizes,tsec(1,:),'-bo'), hold onloglog(datasizes,tsec(2,:),'-k+')set(gca,'xgrid','on'),
set(gca,'ygrid','on'),xlabel('Datasize ->'), ylabel('Runtimes (s)')legend(upper(strrep(fcns,'_',' '))),title('Runtime Plot')figure,
% Plot speedupssemilogx(datasizes,tsec(1,:)./tsec(2,:),'-rx')
set(gca,'ygrid','on'), xlabel('Datasize ->')legend('Speedup(x) with cumsum+diff over cumsum-only'),title('Speedup Plot')rld_cumsum.m:
function out = rld_cumsum(vals,runlens)index = zeros(1,sum(runlens));index([1 cumsum(runlens(1:end-1))+1]) = 1;out = vals(cumsum(index)); return;
運行時和加速圖
結論
cumsum-only
cumsum+diffcumsum-only
cumsum-onlyvalscumsum+diffdiff(vals)nsum(runLengths)cumsum-onlyn
侃侃無極
TA貢獻2051條經驗 獲得超10個贊
index = zeros(1,sum(b));index([1 cumsum(b(1:end-1))+1]) = 1;c = a(cumsum(index));
說明：
bindexa
ab
index = [1 0 1 0 1 1 0 0]cumsum(index) = [1 1 2 2 3 4 4 4] c = [1 1 3 3 2 5 5 5]
編輯：
c = arrayfun(@(x,y) x.*ones(1,y),a,b,'UniformOutput',false);c = [c{:}];添加回答
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