I want to find and save all values greater than 0 in an array and save them in a variable called "times". How do I do that? And what is the difference between saving the indices of those cells versus the actual values of the cells?
This is what I have tried, but it must be worng because I get the error:
Undefined operator '>' for input arguments of type
'cell'.
clear all, close all
[num,txt,raw] = xlsread('test.xlsx');
times = find(raw(:,5)>0)
To access the contents of a cell you must use {} instead of ():
idx = find([raw{:, 5}] > 0);
But this gives you the index of the cells of raw containing a positive value. If you want the values instead, you can access them and collect them in a numeric array in this way:
times = [raw{idx, 5}];
Related
I have a cell array that contains a lot of NaN. But for whatever reason the isnan function can't detect them (hence this doesn't work cellfun(#(Iarray) any(isnan(Iarray)),Iarray);) so I figured it was actually strings that contains NaN.
I perform two things on this array : cleaning empty rows and columns and removing NaN (well trying to).
So I want to replace all the NaN by empty cells and then perform to clean all empty cells with the isempty function. I'll use a loop and if char(x(i,j))=='NaN'.
So here comes my problem I want to empty a cell and then detect that cell with the isempty function but I have no idea how. I have tried x(1,2)= [], x(1,2)= {[]}, x(1,2)='' but none of those gives a 1 for isempty(x(1,2)) for example.
Does anyone know how to solve my problem?
Thanks in advance!
If you want to empty the content of a cell you can use :
x{1,2} = [];
There is a difference between indexing using parentheses () and brackets {}. You can think a cell array as an array of cells that each cell contains a value such as 1 ,2 , []. When a cell is indexed with parentheses it returns the result as cell (or more precisely as an array of type cell) but when it is indexed with brackets it returns the content of the cell (or more precisely as a comma separated list containing the contents of the indexed cells). So when you write such an expression:
x(1,2) = [];
It removes the second element from the array of cells and behaves like indexing other array types. For example when you want to remove the second element of a = [1 2 3] you can use a(2)=[].
But when you write x{1,2} = []; it accesses the content of the cell and sets it to a null array [0 x 0] of type double that is empty.
Likewise a={} is a [0 x 0] null array of cells and b={[]} is an [1 x 1] array of cells that its first element contains a null array [0 x 0] of type double. When you use isempty(b) it returns false because it contains an element and when you use isempty(b(1)) it returns false because b(1) returns an array of cells that contains an element but when you use isempty(b{1}) it returns true because the {} operator extracts the contents of the first cell that is a null array.
In short, cells can be accessed using both () and {}, and based on the situation [] has different functionalities: a) removing element b) null array.
I'm trying to store the color values given by the impixel function into a matrix or an array of some sort.
B = cell(301, 51);
for R = 200: 500
for C = 175 : 225
B(R-199,C-174) = impixel(I,R,C);
end
end
I created a cell array to hold the values, but I keep getting the following error:
"Conversion to cell from double is not possible."
Where is my error? Thanks!
Looking at the documentation of impixel, it states that its outputs are all either of class double or single.
In your code, you define B as a cell array. There is no problem storing the output of impixel in B. However, if you index it with the parenthesis (), it expects the value assigned to also be a cell. You want to assign the output of impixel to a particular element of B, and need to use the curly braces {} to refer to the element. I believe changing your code to
B{R-199,C-174} = impixel(I,R,C);
may solve your issue.
The error should be in this line:
B(R-199,C-174) = impixel(I,R,C);
impixel in this case returned a double type, while B is a cell type.
I've been trying to follow this answer in order to obtain unique strings from a given cell array. However, I'm running into trouble when iterating over these values. I have tried for loops as follows:
[unique_words, ~, occurrences] = unique(words);
unique_counts = hist(occurrences, 1:max(occurrences));
for a=1:numel(unique_words)
word = unique_words{a}
count = unique_counts{a}
result = result + a_struct.(unique_words{a}) + unique_counts{a}
end
When trying to reference the items like this, I receive the error:
Cell contents reference from a non-cell array object.
Changing the curly brackets to round brackets for unique_couts yields the error:
Reference to non-existent field 'N1'.
Changing both unique_words and unique_counts to round brackets yields:
Argument to dynamic structure reference must evaluate to a valid field name.
How am I to iterate over the results of unique?
unique_words is a cell array. unique_counts is a vector. So unique_words should be accessed using curly brackets and unique_counts using round ones. The error that you are getting in this case is related to the a_struct (which is not defined in the question) not having the corresponding field, not the access method.
I have a cell array that is a list of file names. I transposed them because I find that easier to work with. Now I am attempting to go through each line in each cell and remove the lines based on their file extension. Eventually, I want to use this list as file names to import data from. This is how I transpose the list
for i = 1:numel(F);
a = F(1,i);
b{i} = [a{:}'];
end;
The code I am using to try and read the data in each cell keeps giving me the error input must be of type double or string. Any ideas?
for i = 1:numel(b);
for k = 1:numel(b{1,i});
b(cellfun(textscan(b{1,i}(k,1),'%s.lbl',numel(b)),b))=[];
end;
end;
Thanks in advance.
EDIT: This is for MATLAB. Should have been clear on that. Thanks Brian.
EDIT2: whos for F is
Name Size Bytes Class Attributes
b 1x11 13986188 cell
while for a is
Name Size Bytes Class Attributes
a 1x1 118408 cell
From your description I am not certain how your F array looks, but assuming
F = {'file1.ext1', 'file2.ext2', 'file3.ext2', 'file2.ext1'};
you could remove all files ending with .ext2 like this:
F = F(cellfun('isempty', regexpi(F, '\.ext2$')));
regexpi, which operates on each element in the cell array, returns [] for all files not matching the expression. The cellfun call converts the cell array to a logical array with false at positions corresponding to files ending with .ext2and true for all others. The resulting array may be used as a logical index to F that returns the files that should be kept.
You're using cellfun wrong. It's signature is [A1,...,Am] = cellfun(func,C1,...,Cn). It takes a function as first argument, but you're passing it the result of textscan, which is a cell array of the matching strings. The second argument is a cell array as it should be, but it doesn't make sense to call it over and over in a loop. `cellfun´'s job is to write the loop for you when you want to do the same thing to every cell in a cell array.
Instead of parsing the filename yourself with textscan, I suggest you use fileparts
Since you're already looping over the cell array in transpose-step, it might make sense to do the filtering there. It might look something like this:
for i = 1:numel(F);
a = F(1,i);
[~,~,ext] = fileparts(a{:});
if strcmpi(ext, '.lbl')
b{i} = [a{:}'];
end
end;
I want to replace the value of the fields in a structure array. For example, I want to replace all 1's with 3's in the following construction.
a(1).b = 1;
a(2).b = 2;
a(3).b = 1;
a([a.b] == 1).b = 3; % This doesn't work and spits out:
% "Insufficient outputs from right hand side to satisfy comma separated
% list expansion on left hand side. Missing [] are the most likely cause."
Is there an easy syntax for this? I want to avoid ugly for loops for such simple operation.
Credits go to #Slayton, but you actually can do the same thing for assigning values too, using deal:
[a([a.b]==1).b]=deal(3)
So breakdown:
[a.b]
retrieves all b fields of the array a and puts this comma-separated-list in an array.
a([a.b]==1)
uses logical indexing to index only the elements of a that satisfy the constraint. Subsequently the full command above assigns the value 3 to all elements of the resulting comma-separated-list according to this.
You can retrieve that the value of a field for each struct in an array using cell notation.
bVals = {a.b};
bVals = cell2mat( bVals );
AFAIK, you can't do the same thing for inserting values into an array of structs. You'll have to use a loop.