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.
Related
I have the following code:
Xh = zeros(InfDS.statedim,N);
Xh(:,1) = str2double(states_0(2:end,2));
Px = diag(str2double(states_0(2:end,3)));
Where states_0 is a Nx3 cell array. It could for instance look as follows:
'' 'x0' 'P0'
'SOC' '100' '0.75'
'RI' '0.001' '0.75'
but it could also contain more parameters.
My issue is that I have rewritten part of the code, s.t. in no longer return a cell array containing strings, but a cell array containing doubles.
[ 100] [0.7500]
[1.0000e-03] [0.7500]
I figured this would be easier to work with due to the fewer conversions, but it seems not to be... I have tried:
Xh = zeros(InfDS.statedim,N);
Xh(:,1) = states_0(1:end,1);
Px = diag(states_0(1:end,2));
but that gives me the error:
Conversion to double from cell is not possible.
Error in testfile (line 61)
Xh(:,1) = states_0(1:end,1);
Could someone explain why this is the case? I figured this would be a better way of doing things, but it seems outright illegal...
It seems like cell2mat() does the trick!
Note: I guess string2double implicitly converts to an array?
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}];
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;
My question is easily summarized as: "Why does the following not work?"
teststruct = struct('a',3,'b',5,'c',9)
fields = fieldnames(teststruct)
for i=1:numel(fields)
fields(i)
teststruct.(fields(i))
end
output:
ans = 'a'
??? Argument to dynamic structure reference must evaluate to a valid field name.
Especially since teststruct.('a') does work. And fields(i) prints out ans = 'a'.
I can't get my head around it.
You have to use curly braces ({}) to access fields, since the fieldnames function returns a cell array of strings:
for i = 1:numel(fields)
teststruct.(fields{i})
end
Using parentheses to access data in your cell array will just return another cell array, which is displayed differently from a character array:
>> fields(1) % Get the first cell of the cell array
ans =
'a' % This is how the 1-element cell array is displayed
>> fields{1} % Get the contents of the first cell of the cell array
ans =
a % This is how the single character is displayed
Since fields or fns are cell arrays, you have to index with curly brackets {} in order to access the contents of the cell, i.e. the string.
Note that instead of looping over a number, you can also loop over fields directly, making use of a neat Matlab features that lets you loop through any array. The iteration variable takes on the value of each column of the array.
teststruct = struct('a',3,'b',5,'c',9)
fields = fieldnames(teststruct)
for fn=fields'
fn
%# since fn is a 1-by-1 cell array, you still need to index into it, unfortunately
teststruct.(fn{1})
end
Your fns is a cellstr array. You need to index in to it with {} instead of () to get the single string out as char.
fns{i}
teststruct.(fns{i})
Indexing in to it with () returns a 1-long cellstr array, which isn't the same format as the char array that the ".(name)" dynamic field reference wants. The formatting, especially in the display output, can be confusing. To see the difference, try this.
name_as_char = 'a'
name_as_cellstr = {'a'}
You can use the for each toolbox from http://www.mathworks.com/matlabcentral/fileexchange/48729-for-each.
>> signal
signal =
sin: {{1x1x25 cell} {1x1x25 cell}}
cos: {{1x1x25 cell} {1x1x25 cell}}
>> each(fieldnames(signal))
ans =
CellIterator with properties:
NumberOfIterations: 2.0000e+000
Usage:
for bridge = each(fieldnames(signal))
signal.(bridge) = rand(10);
end
I like it very much. Credit of course go to Jeremy Hughes who developed the toolbox.