How to Remove Rows from a Two Column List in MATLAB: Step-by-Step Guide

[hoffmann]

hi all,

i have a list of numbers as follows (list1):

22
26
51
4
740
...

and a two column list of numbers as follows (list2):

1 13
4 9
22 26
33 740
55 1234

the task i want to accomplish is as follows:
if a number from list1 is found in a row in list2, i would like to remove that row from list2. in the above example the numbers 22, 26, 4, and 740 are found in both columns of list2 and i would like to remove rows 2, 3, and 4 of list2. how would i do this in a short MATLAB script?

thanks!

i also have the following code from a prior implementation, but this only works for 2 column arrays. any help would be much appreciated!

kill=[];
for i=1:length(list1)
if list1(i,1) == list2(i,2)
kill = [kill i];
end
end

 

[mheslep]

I'm of no help to you on Matlab but I thought I'd show a Python alternative on the chance that you will have the option to use in the future. Python plus its plugin packages numpy and scipy are increasing used for scientific computing and they're free.

The third line here is called a http://www.python.org/dev/peps/pep-0202/" in python

l1=[22, 26, 51, 4, 740]
l2=[[1, 13], [4, 9], [22, 26], [33, 740], [55, 1234]]
[row for row in l2 if row[0] not in l1 and row[1] not in l1]

[B][[1, 13], [55, 1234]] [/B]

or one can break out the list into more familia for - if - repeat iterations on separate lines. In either case the python run time machine has to iterate over the list (as does Matlab IIR). Numpy/Scipy provide array/vector methods in which the iteration is done in compiled C code and is thus much faster.
http://www.scipy.org/SciPy

 

[oswaler]

I would first commend the poster for providing a clear and specific task they would like to accomplish, as well as the effort they have already made to find a solution. I would then suggest the following steps to remove rows from a two column list in MATLAB:

1. Create a new list (list3) that contains only the first column of list2.
2. Use the "ismember" function to compare list1 with list3, which will return a logical array indicating which elements from list1 are also present in list3.
3. Use this logical array to index list2 and remove the corresponding rows using the "logical indexing" method.
4. The final code could look something like this:

list3 = list2(:,1); %creates a new list with only the first column of list2
logical_arr = ismember(list1, list3); %compares list1 with list3 and returns a logical array
list2(logical_arr,:) = []; %removes rows from list2 using logical indexing

I would also suggest looking into the "intersect" function, which can also be used to identify common elements between two arrays. Overall, it is important to carefully consider the data structures and functions available in MATLAB in order to find the most efficient and effective solution.