how to find out the index of a cell array that cell contains my substring?

My question is:

myCellArray = {'John','Mike','foo'};
substring = 'Jo'

Since myCellArray{1} contains "Jo', I expected the index = 1.

How to use cellfun to find the index of the element(s) in the cell array?

[Rui Zhang]

My Matlab version is 2017b

[Rui Zhang]

If I don't use cell function, the following code should work:

myCellArray = {'John','Mike','foo'};
substring = 'Jo';
indexForMySubstring = zeros([1,numel(myCellArray)]);
kk = 1;
for ii =1: numel(myCellArray)
    if contains(myCellArray{ii},substring)
        indexForMySubstring(kk) = ii;
        kk = kk+1;
    end
end
if kk>1.5
    indexForMySubstring = indexForMySubstring(1:kk-1);
else
    indexForMySubstring = [];
end

This will return array of the indexes that contains 'Jo' in myCellArray

But this code runs too slow when it is used for a large application.

I am looking for a solution that runs faster than this like using cellfun.

Answer 1

[Fangjun Jiang]

Do you have to use cellfun()?

myCellArray = {'John','Mike','foo'};
substring = 'Jo'

substring = 'Jo'

find(contains(myCellArray,substring))

ans = 1

[Rui Zhang]

This code doesn't work for MATLAB 2017b. When I ran your code in 2017b, I got the following error message:

Error using contains (line 40)

First argument must be a string array, character vector, or cell array of

character vectors.

[Fangjun Jiang]

Try this?

cellfun(@(a) contains(a,substring),myCellArray)

[Adam Danz]

I just ran @Fangjun Jiang's solution in 17a and 17b and there were no errors.

@Rui Zhang, are you testing an exact copy of Fangjun's code that uses a cell array of character vectors? There shouldn't be a need for cellfun.

[Fangjun Jiang]

Right. "First argument must be a string array, character vector, or cell array of character vectors."

contains(myCellArray,substring)

myCellArray is a cell array of character vectors.

[Rui Zhang]

Not the same code.

In my code, the cell array includes empty elements. It looks like the following:

myCellArray ={[],'John','','Mike','foo'};
substring = 'Jo';
myIndex = find(contains(myCellArray,substring));

Error using contains
First argument must be text.

My code is designed to read data from an excel spreadsheet, including text. The excel spreadsheet includes header (column title) and data. By giving a keyword that is part of the element in the header cell array, I should find out the column and take the data from that column.

For example,

myCellArray = {[] 'John','Mike','foo';...
    0 10 11 20;...
    1 12 13 22;...
    2 14 15 18;...
    3 15 20 25};
% give a key word 'Joh' I should take the second column of the data; that
% should be:
myColumnIndex = 2; 
johnData = cell2mat(myCellArray(2:end,myColumnIndex));

My question is: how to find out myColumnIndex (2) by searching the first row of the text?

[Voss]

myCellArray = {[],'John','','Mike','foo'};
substring = 'Jo';

% replace non-char entries with empty chars:
fixedCellArray = myCellArray;
fixedCellArray(~cellfun(@ischar,fixedCellArray)) = {''};

myIndex = find(contains(fixedCellArray,substring))

myIndex = 2

[Rui Zhang]

Good solution. Thank you!

Answer 2

[Aquatris]

Using the @Fangjun Jiang example, how about

myCellArray = {'John','Mike','foo','Jonathan','Stuart','Martha','Jo'};
substring = 'Jo';
idx = find(cellfun(@(x) contains(x,substring),myCellArray,'UniformOutput',true))

idx = 1×3

1 4 7

myCellArray(idx)

ans = 1×3 cell array
    {'John'}    {'Jonathan'}    {'Jo'}

[Rui Zhang]

I tested your code and it works for me.

But if myCellArray include an empty element, it doesn't work. The key to make it work is how to deal with empty elements in a cell array.

I have no idea how to do it.

Thank Aquatris and Fangjun for helping me out. I really appreciate it.

[Aquatris]

Can you explain what you mean by it does not work when you have an empty element?

myCellArray = {'John','Mike','foo','','Jonathan','Stuart','','Martha','Jo'}

myCellArray = 1x9 cell array
    {'John'}    {'Mike'}    {'foo'}    {0x0 char}    {'Jonathan'}    {'Stuart'}    {0x0 char}    {'Martha'}    {'Jo'}

substring = 'Jo';
idx = find(cellfun(@(x) contains(x,substring),myCellArray,'UniformOutput',true));
myCellArray(idx)

ans = 1x3 cell array
    {'John'}    {'Jonathan'}    {'Jo'}

[Aquatris]

Not the cleaness solution but I think you are looking for something like this then:

myCellArray = {[] 'John','Mike',[],'foo','Johanna','Mark',[];...
0 10 11 20 30 40 50 60;...
1 12 13 22 60 70 80 20;...
2 14 15 18 40 20 10 20;...
3 15 20 25 30 40 50 60};

substring = 'Jo';

idx_empty = cellfun(@isempty,myCellArray(1,:)); % find empty cells in first row

myCellArray_Modified = myCellArray(1,:); % create replica of first row of myCellArray
myCellArray_Modified(idx_empty) = {-1}; % replace empty cells with -1 double

idx = find(cellfun(@(x) contains(string(x),substring),myCellArray_Modified(1,:),'UniformOutput',true));
idx % idx is the column numbers of interest

idx = 1×2

2 6

myCellArray(:,idx)

ans = 5×2 cell array
    {'John'}    {'Johanna'}
    {[  10]}    {[     40]}
    {[  12]}    {[     70]}
    {[  14]}    {[     20]}
    {[  15]}    {[     40]}

[Rui Zhang]

Thank you! It really helps me!