Remove empty rows from matrix

Hi folks,

I have the following matrix:

0.6857    0.1248    0.9636    1.0884    0.4807    0.6077    0.3644         0         0         0
    0.9093    1.0006    1.0006    1.0006    1.0006    0.3702         0         0         0         0
    0.6367    1.0106    0.5669    0.4437    1.0106    1.0106    0.4608         0         0         0
    0.2100    0.3250    1.1000    0.9750    0.1250    1.1000    0.4070         0         0         0
    0.2048    0.4401    0.7116    1.1518    0.1521    0.2741         0         0         0         0
    0.5575    0.2119    1.2212    0.3091    0.9121    0.8300    0.0993         0         0         0
    0.6041    1.0239    0.6050    0.4189    1.0239    0.3428         0         0         0         0
    0.5817    1.0205    0.4559    0.5645    1.0205    0.3417         0         0         0         0
    0.9277    1.0209    0.5690    0.4519    1.0209    1.0209    0.4390         0         0         0
    0.1817    1.0217    0.7974    0.2243    0.4393         0         0         0         0         0
    0.4787    0.9174    0.2224    1.1398    0.7216    0.4182    0.3816         0         0         0
    0.9091    1.0004    1.0004    1.0004    1.0004    0.5803         0         0         0         0
    0.2126    1.0104    0.1849    1.1953    0.4451    0.2482         0         0         0         0
    0.2531    0.2652    1.0657    1.0657    0.4962    0.5695    0.7034         0         0         0
    0.2072    0.8844    0.2805    1.1650    0.5038    0.2651         0         0         0         0
    0.3229    1.0774    0.0362    1.1136    1.1136    0.0092    0.3636         0         0         0
    0.2172    1.2212    0.0671    1.1541    0.5882    0.2788         0         0         0         0
    0.3084    1.0633    1.0633    0.3386    0.4706         0         0         0         0         0
    0.2108    1.0037    1.0037    1.0037    0.3361         0         0         0         0         0
    0.1521    0.0784    1.0078    1.0862    0.4669    0.6193    0.3637         0         0         0
    0.9111    1.0026    1.0026    1.0026    1.0026    0.8622         0         0         0         0
    0.1406    1.0046    1.0046    1.0046    1.0046    1.0046    1.0046    0.5075         0         0
    0.1918    0.0487    1.0297    1.0784    0.5640    0.3634         0         0         0         0
    0.1513    0.0229    1.2441    0.4140    0.8301    0.8509    0.0958         0         0         0
    0.8749    1.0001    1.0001    0.0422         0         0         0         0         0         0
    0.8900    1.0173    0.5089    0.5084    1.0173    1.0173    0.5565         0         0         0
    0.8903    1.0177    0.7745         0         0         0         0         0         0         0
    1.0498    0.0125    1.2351    0.4561    0.7790    0.4136         0         0         0         0
    1.0150    0.7605    0.4198    0.8982         0         0         0         0         0         0
    0.1808    1.0165    1.0165    1.0165    0.1931         0         0         0         0         0
    0.8158    1.0071    0.2857    0.4807         0         0         0         0         0         0
    0.8973    0.2251    0.9714    0.8502    0.3462    0.4006         0         0         0         0
    0.2134    1.2000    0.1495    1.0506    0.7584    0.4417    0.3000         0         0         0
    0.7503    1.0005    1.0005    1.0005    1.0005    0.5472         0         0         0         0
    0.8519    1.1359    0.0001    0.8643         0         0         0         0         0         0
    0.7315    0.4265    0.7546    0.3955         0         0         0         0         0         0
    0.6675    0.8202         0         0         0         0         0         0         0         0
    0.3814    1.0037    1.0037    1.0037    0.5490         0         0         0         0         0
    0.3608    1.0934    0.0694    0.2967         0         0         0         0         0         0
    0.1815    1.0204    1.0204    1.0204    1.0204    0.0804    0.6033         0         0         0
    0.3523    1.0676    1.0676    0.0248    1.0429    0.5840         0         0         0         0
    0.3721    0.6114    0.6717    0.4296         0         0         0         0         0         0
    0.1866    1.0493    1.0493    0.5664    0.4830    1.0493    0.7450         0         0         0
    0.2975    1.0260    0.0635    0.9624    1.0260    0.5612         0         0         0         0
    0.3385    0.8884         0         0         0         0         0         0         0         0
    0.2690    0.8727    0.3151    0.3977         0         0         0         0         0         0
    0.2374    1.0482    0.7679    0.2802    1.0482    0.5733         0         0         0         0
    0.1428    1.0986    0.2470    0.1208         0         0         0         0         0         0
    0.1407    1.0821    1.0821    0.1822    0.8999    0.5919         0         0         0         0
    0.1300    0.7610         0         0         0         0         0         0         0         0
    0.9675    0.0053    0.4343         0         0         0         0         0         0         0
    0.1817    1.0220    1.0220    1.0220    0.9418    0.0802    1.0220    0.2555         0         0
    0.8054    1.0738    0.0971    0.9767    0.5874         0         0         0         0         0
    0.7961    0.2463    0.5288         0         0         0         0         0         0         0
    0.6895    0.6923    0.3524    1.0447    0.5715         0         0         0         0         0
    0.6871         0         0         0         0         0         0         0         0         0
    0.9155         0         0         0         0         0         0         0         0         0
    0.4147         0         0         0         0         0         0         0         0         0
    0.7308    0.0113    1.1596    0.8044    0.3522         0         0         0         0         0
    0.6601    0.3453         0         0         0         0         0         0         0         0
    0.5076    0.0782         0         0         0         0         0         0         0         0
    0.7649    0.2744    0.5651         0         0         0         0         0         0         0
    0.6115    0.3237    0.1214         0         0         0         0         0         0         0
    0.7236    0.0776    0.6387         0         0         0         0         0         0         0
    0.5311    0.1151    0.9963         0         0         0         0         0         0         0
    0.1641    0.0599    0.9660    1.0259    0.5612         0         0         0         0         0
    0.8965         0         0         0         0         0         0         0         0         0
    0.6188    1.0043    0.1607         0         0         0         0         0         0         0
    0.4533    0.3284    0.9263         0         0         0         0         0         0         0
    0.3628    0.4568    0.4365         0         0         0         0         0         0         0
    0.2558    0.5884         0         0         0         0         0         0         0         0
    0.1884    0.4902         0         0         0         0         0         0         0         0
    0.1455    0.0447    0.5526         0         0         0         0         0         0         0
    0.0793    0.3838         0         0         0         0         0         0         0         0
    0.0805    1.0149    0.6064         0         0         0         0         0         0         0
    0.7523    0.8290    0.2982    1.1272    0.5694         0         0         0         0         0
    0.1034    0.9373    0.3661    1.1931    0.1102    0.7427         0         0         0         0
    0.0888    0.4431    0.6763    0.0638         0         0         0         0         0         0
    0.0670    0.3839         0         0         0         0         0         0         0         0
    0.0681    1.0164    0.6073         0         0         0         0         0         0         0
    0.0755    0.4427    0.6843    0.0642         0         0         0         0         0         0
    0.5619    0.4598    0.6869    1.1467    0.2045         0         0         0         0         0
    0.4987    0.3906         0         0         0         0         0         0         0         0
    0.5430    0.0114    1.0968    0.0632         0         0         0         0         0         0
    0.4407    0.4027         0         0         0         0         0         0         0         0
    0.4495    1.0963    0.2350    0.8613    0.5538         0         0         0         0         0
    0.5038    0.4028         0         0         0         0         0         0         0         0
    0.4943    0.0541    1.1424    0.0651         0         0         0         0         0         0
    0.6954    0.4171         0         0         0         0         0         0         0         0
    0.4677    0.2769    1.1634    0.0663         0         0         0         0         0         0
    0.1589    1.1350    0.2493    0.8856    0.5733         0         0         0         0         0
    0.3814    0.0163    1.2831    0.0731         0         0         0         0         0         0
    0.6389    1.0369    0.4251         0         0         0         0         0         0         0
    0.0710    1.0149    0.5551         0         0         0         0         0         0         0
    0.4376    0.6881    1.0147         0         0         0         0         0         0         0
    0.6393    1.1416    0.2036         0         0         0         0         0         0         0
    0.3888    1.0800    0.1926         0         0         0         0         0         0         0
    0.6852    0.3812         0         0         0         0         0         0         0         0
    0.4217    0.7882    0.3831    0.6674         0         0         0         0         0         0
    0.2469    1.0330    0.1550    0.2272         0         0         0         0         0         0
    0.6003    0.1677    0.6004         0         0         0         0         0         0         0
    0.3019    0.1893    1.0737    0.5634    0.0933         0         0         0         0         0
    0.8692    0.1094    0.5962         0         0         0         0         0         0         0
    0.3294    0.5862    0.7919    0.6614    0.0828         0         0         0         0         0
    0.3616    1.1205    0.0095    0.5708         0         0         0         0         0         0
    0.9761    0.2160    0.9891    0.4625         0         0         0         0         0         0
    0.1902    1.0011    0.5057         0         0         0         0         0         0         0
    0.2418    1.0338    1.0338    0.5295         0         0         0         0         0         0
    0.2351    1.0051    0.1556    0.8495    0.4699         0         0         0         0         0
    0.2517    1.0759    1.0233    0.0526    0.5968         0         0         0         0         0
    0.2342    1.0014    1.0014    0.4238         0         0         0         0         0         0
    0.2430    1.0389    0.9815    0.0574    0.4320         0         0         0         0         0
    0.2707    0.5728    0.5845    1.1573    0.2449    0.2636         0         0         0         0
    0.1065    0.1941    1.2852    0.1126    1.1726    0.4194    0.2113         0         0         0
    0.5830    0.5932         0         0         0         0         0         0         0         0
    0.4807    0.7002    0.5100    1.2102    0.0551    0.4094         0         0         0         0
    0.8563    0.0122    0.5702         0         0         0         0         0         0         0
    0.1487    0.9660    0.3856    0.3652         0         0         0         0         0         0
    0.7246    0.1034    0.4980         0         0         0         0         0         0         0
    0.2777    0.7889    0.3046         0         0         0         0         0         0         0

    Columns 11 through 20

           0         0         0         0         0         0         0         0         0         0   
           0         0         0         0         0         0         0         0         0         0    
           0         0         0         0         0         0         0         0         0         0

I want to remove all the rows which are all zeros.

Thanks

[Stephen23]

None of the rows are all zeros.

Answer 1

[Star Strider]

If ‘M’ is your matrix, this works:

M = M(~all(M == 0, 2),:);

It will remove the ‘all zero’ rows using ‘logical indexing’.

[Harry Saner]

This was really helpful thanks!

what does the 2 do or mean? I can see that it's basically saying for M the rows of the matrix M "not all" the elements that are equal to 0 must be removed

but how would you explain each part of that line of code in words?

[Star Strider]

My pleasure!

The code assigns to ‘M’ the rows of the original ‘M’ that do not have all the elements of each row equal to 0.

It has the effect of elimiinating the rows in which all the elements of the row are equal to 0. The ‘2’ dimension argument to the all function tells the all function to look along the rows (rather than the columns, that would be the default dimension 1). The first part of the code:

~all(M == 0, 2)

creates the logical row index, and the code assigna all the columns in the original matrix (using the wildcard ‘:’) where the row argument logical index is true, or logical 1.

[Thiago de Aquino Costa Sousa]

And what if, instead of 0 I have empty [] cells??? How can I remove them?

[Voss]

@Thiago de Aquino Costa Sousa: If you have a cell array (not a matrix as in the question) and you want to remove those rows whose elements all contain the empty array [], then you can do this:

% a cell array with some cells containing empty arrays []:
C = {1 [] 3; [] [] []; [7 8] [] []}

C = 3×3 cell array
    {[       1]}    {0×0 double}    {[       3]}
    {0×0 double}    {0×0 double}    {0×0 double}
    {[     7 8]}    {0×0 double}    {0×0 double}

C = C(~all(cellfun(@isempty,C),2),:)

C = 2×3 cell array
    {[  1]}    {0×0 double}    {[       3]}
    {[7 8]}    {0×0 double}    {0×0 double}