I want to import some data in an m file. So for I have managed to create a cell array of the data. I want to convert it into a matrix. I used cell2mat but I get an error. I'm new to Matlab, so I would like some help. Here is my complete code
fid = fopen('vessel-movements.csv');
C = textscan(fid, '%f %f %f %f %f %s %s %s', 'HeaderLines', 1, 'Delimiter', ',')
fclose(fid);
iscell(C)
T = cell2mat(C)
The answer I get is:
C =
Columns 1 through 4
[300744x1 double] [300744x1 double] [300744x1 double] [300744x1 double]
Columns 5 through 8
[300744x1 double] {300744x1 cell} {300744x1 cell} {300744x1 cell}
ans =
1
??? Error using ==> cell2mat at 46
All contents of the input cell array must be of the same data type.
Error in ==> test at 5
T = cell2mat(C)
My question is how I can do that? The data is in the following link vessel-movements.csv. It contains numbers, as ids and coordinates, and timestamps.
As the error message says:
All contents of the input cell array must be of the same data type.
Columns 6, 7 and 8 are chars (datestrings). It's not possible to convert them into a Matrix. Leave them in a cell.
You can transform only the numerical data into a matrix: data = cell2mat(C(:,1:5)). The three left columns have to be converted with datenum() into a numerical time to add it to data matrix.
When you've got >=R2013b, you can use as datatype a table like: data = readtable('vessel-movements.csv');
I assume you only want to convert the first five columns of C, which are the ones that contain numeric data. You can use cell2mat as follows:
M = cell2mat(C(:,1:5));
or equivalently
M = [C{:,1:5}];
The main difference between a matrix and a cell array (in MATLAB parlance) is that a matrix holds elements of the same type and size, while a cell array holds elements of different types and sizes.
You read numbers and strings. The numbers do have the same type and size (double, 1×1) while the strings are different (they're all char type, but usually different sizes).
To group your numeric data, you must select only the numeric elements of your cell array:
N = horzcat(C{1:5});
while for the strings you should keep the cell array structure:
S = horzcat(C{6:8});
Later edit: Since you admit that you're new to MATLAB, I'm going to make a general recommendation: every time you see a function that you don't know what it does—or behaves unexpectedly from your point of view—mark its name and press F1. The MATLAB documentation is quite comprehensive, and contains also lots of examples depicting the typical uses for that function.
Related
I have a cell array [5x1] which all cells are column vectors such as:
exInt =
[46x1 double]
[54x1 double]
[40x1 double]
[51x1 double]
[ 9x1 double]
I need to have a vector (vec) containing the cells in extInt I need to extract and then I have to convert these into a single column array. Such as:
vec = [1,3];
Output = cell2mat(extInt{vec})
Output should become something an array [86x1 double].
The way I have coded I get:
Error using cell2mat
Too many input arguments.
If possible, I would like to have a solution not using a loop.
The best approach here is to use cat along with a comma-separted list created by {} indexing to yield the expected column vector. We specify the first dimension as the first argument since you have all column vectors and we want the output to also be a column vector.
out = cat(1, extInt{vec})
Given your input, cell2mat attempts to concatenate along the second dimension which will fail for your data since all of the data have different number of rows. This is why (in your example) you had to transpose the data prior to calling cell2mat.
Update
Here is a benchmark to compare execution times between the cat and cell2mat approaches.
function benchit()
nRows = linspace(10, 1000, 100);
[times1, times2] = deal(zeros(size(nRows)));
for k = 1:numel(nRows)
rows = nRows(k);
data = arrayfun(#(x)rand(randi([10, 50], 1), 1), 1:rows, 'uni', 0);
vec = 1:2:numel(data);
times1(k) = timeit(#()cat_method(data, vec));
data = arrayfun(#(x)rand(randi([10, 50], 1), 1), 1:rows, 'uni', 0);
vec = 1:2:numel(data);
times2(k) = timeit(#()cell2mat_method(data, vec));
end
figure
hplot(1) = plot(nRows, times1 * 1000, 'DisplayName', 'cat');
hold on
hplot(2) = plot(nRows, times2 * 1000, 'DisplayName', 'cell2mat');
ylabel('Execution Times (ms)')
xlabel('# of Cell Array Elements')
legend(hplot)
end
function out = cat_method(data, vec)
out = cat(1, data{vec});
end
function out = cell2mat_method(data, vec)
out = cell2mat(data(vec)');
end
The reason for the constant offset between the two is that cell2mat calls cat internally but adds some additional logic on top of it. If you just use cat directly, you circumvent that additional overhead.
You have a small error in your code
Change
Output = cell2mat(extInt{vec});
to
Output = cell2mat(extInt(vec));
For cells, both brackets and parentheses can be used to get information. You can read some more about it here, but to summarize:
Use curly braces {} for setting or getting the contents of cell arrays.
Use parentheses () for indexing into a cell array to collect a subset of cells together in another cell array.
In your example, using brackets with index vector vec will produce 2 separate outputs (I've made a shorter version of extInt below)
extInt = {[1],[2 3],[4 5 6]};
extInt{vec}
ans =
1
ans =
4 5 6
As this is 2 separate outputs, it will also be 2 separate input to the function cell2mat. As this function only takes one input you get an error.
One alternative is in your own solution. Take the two outputs and place them inside a new (unnamed) cell
{extInt{vec}}
ans =
[1] [1x3 double]
Now, this (single) result goes into cell2mat without a problem.
(Note though that you might need to transpose your result before depending on if you have column or row vectors in your cell. The size vector (or matrix) to combine need to match/align.)
Another way as to use parentheses (as above in my solution). Here a subset of the original cell is return. Therefore it goes directly into the cell2matfunction.
extInt(vec)
ans =
[1] [1x3 double]
I have been messing around and I got this working by converting this entry into a new cell array and transposing it so the dimensions remained equivalent for the concatenating process
Output = cell2mat({extInt{vec}}')
use
Output = cell2mat(extInt(vec))
Since you want to address the cells in extInt not the content of the cells
extInt(vec)
extInt{vec}
try those to see whats going on
I want to change a matrix N*123456 to a cells of cells, each sub-cell contains a N*L matrix
Eg:
matrixSize= 50*123456
N=50
L=100
Output will be 1*1235 cell and each cell has a 50*L matrix (last cell has only 50*56)
I know there is a function mat2cell in matlab:
Output = mat2cell(x, [50], [100,100,100,......56])
But it doesn't sound an intuitive solution.
So is there a good solution?
If I understand you correctly, assuming your matrix is denoted m, this is what you wanted:
a=num2cell(reshape(m(:,1:size(m,2)-mod(size(m,2),L)),N*L,[]),1);
a=cellfun(#(n) reshape(n,N,L), a,'UniformOutput',false);
a{end+1}=m(:,end-mod(size(m,2),L)+1:end);
(this can be shortened to a single line if you wish)...
Lets test with some minimal numbers:
m=rand(50,334);
N=50;
L=100;
yields:
a =
[50x100 double] [50x100 double] [50x100 double] [50x34 double]
note that I didn't check for the exact dimension in the reshape, so you may need to reshape to ...,[],N*L) etc.
Just use elementary maths.
q = floor(123456/100);
r = rem(123456,100);
Output = mat2cell(x, 50, [repmat(100,1,q),r])
i have a cell of several matrices (all double and with the same dimension)
my_cell =
[172x15 double] [172x15 double] [172x15 double] [172x15 double]
I would to write the matrices on txt file side by side and tabulated, to obtain a .txt file with 172 rows and 60 columns (in this case)
use dlmwrite and cell2mat
mat = cell2mat(my_cell);
delimiter = ' '; % // used to separate two values in a row in the file
filename = 'test.txt';
dlmwrite(filename,mat,delimiter);
>> dlmwrite('file1.txt', [c{:}],'delimiter','\t','precision','%.5f')
or
>> dlmwrite('file2.txt', c(:)','delimiter','\t','precision','%.5f')
You have to choose a precision, otherwise you'll get non-uniform lines because of different numbers of decimal places.
Code
%// output_filepath is the name of your output text file
c1 = horzcat(my_cell{:})
datacell = mat2cell(c1,ones(1,size(c1,1)),ones(1,size(c1,2)))
dlmwrite(output_filepath,datacell,'\t'); %// a TAB delimiter is used
I have a semicolon separated file in the following format:
Press;Temp.;CondF;Cond20;O2%;O2ppm;pH;NO3;Chl(a);PhycoEr;PhycoCy;PAR;DATE;TIME;excel.date;date.time
0.96;20.011;432.1;431.9;125.1;11.34;8.999;134;9.2;2.53;1.85;16.302;08.06.2011;12:01:52;40702;40702.0.5
1;20.011;433;432.8;125;11.34;9;133.7;8.19;3.32;2.02;17.06;08.06.2011;12:01:54;40702;40702.0.5
1.1;20.012;432.7;432.4;125.1;11.34;9;133.8;8.35;2.13;2.2;19.007;08.06.2011;12:01:55;40702;40702.0.5
1.2;20.012;432.8;432.5;125.2;11.35;9.001;133.8;8.45;2.95;1.95;21.054;08.06.2011;12:01:56;40702;40702.0.5
1.3;20.012;432.7;432.4;125.4;11.37;9.002;133.7;8.62;3.17;1.87;22.934;08.06.2011;12:01:57;40702;40702.0.5
1.4;20.007;432.1;431.9;125.2;11.35;9.003;133.7;9.48;4.17;1.6;24.828;08.06.2011;12:01:58;40702;40702.0.5
How can I parse this into a matrix in matlab? I don't care about the first row, but I would like the rest of the rows in the matrix. They don't need to be converted into doubles, the matrix can be comprised of strings. There are new lines in the file, which represent the end of a row. There are no semicolons before the new lines.
Thanks for the help.
Consider this code to read the data:
fid = fopen('file.txt','rt');
frmt = [repmat('%f ',1,12) '%s %s %f %s'];
C = textscan(fid, frmt, 'Delimiter',';', 'CollectOutput',true, 'HeaderLines',1);
fclose(fid);
First we read into the variable C the different components: the first twelve columns as numbers, next two as strings (we will convert them to serial date numbers in the next step), another numeric column, and finally a string one:
>> C
C =
[6x12 double] {6x2 cell} [6x1 double] {6x1 cell}
As I mentioned, we can parse and covert C{2} into a serial date:
dt = datenum(strcat(C{2}(:,1),{' '},C{2}(:,2)), 'dd.mm.yyyy HH:MM:ss');
Now we can merge all of them into a cell array as a table. We use a cell array instead of a numeric matrix because the last column is still strings.
>> data = [num2cell([C{1} dt C{3}]) C{4}]
data =
Columns 1 through 7
[0.96] [20.011] [432.1] [431.9] [125.1] [11.34] [8.999]
[ 1] [20.011] [ 433] [432.8] [ 125] [11.34] [ 9]
[ 1.1] [20.012] [432.7] [432.4] [125.1] [11.34] [ 9]
[ 1.2] [20.012] [432.8] [432.5] [125.2] [11.35] [9.001]
[ 1.3] [20.012] [432.7] [432.4] [125.4] [11.37] [9.002]
[ 1.4] [20.007] [432.1] [431.9] [125.2] [11.35] [9.003]
Columns 8 through 14
[ 134] [ 9.2] [2.53] [1.85] [16.302] [7.3466e+05] [40702]
[133.7] [8.19] [3.32] [2.02] [ 17.06] [7.3466e+05] [40702]
[133.8] [8.35] [2.13] [ 2.2] [19.007] [7.3466e+05] [40702]
[133.8] [8.45] [2.95] [1.95] [21.054] [7.3466e+05] [40702]
[133.7] [8.62] [3.17] [1.87] [22.934] [7.3466e+05] [40702]
[133.7] [9.48] [4.17] [ 1.6] [24.828] [7.3466e+05] [40702]
Column 15
'40702.0.5'
'40702.0.5'
'40702.0.5'
'40702.0.5'
'40702.0.5'
'40702.0.5'
You can use textscan for this.
fid = fopen('data.txt'); %open file
headers = fgetl(fid); %get first line
headers = textscan(headers,'%s','delimiter',';'); %read first line
format = repmat('%s',1,size(headers{1,1},1)); %count columns and make format string
data = textscan(fid,format,'delimiter',';'); %read rest of the file
data = [data{:}];
Evening Max.
I'm going to assume that you are already able to import the data from a file or otherwise get it into Matlab. The method that I normally use for data like this leaves it in a column matrix of cells. Each cell then contains a line of data from the file.
You can then convert the cell to a matrix of characters and use regexp to parse that data into an easier to use matrix with the top row being your header data.
If you get stuck just post up some code and we can work through it.
Cheers!
Update:
Here's the code I was talking about.
A = importdata('filepath\sample.txt') %This uses the newline on each line to make a new row.
B= [];
for(n = 1:size(A,1))
B = [B;regexp(cell2mat(A(n)),';','split')]; %This uses the ; to split the string
end
Matlab indexing is always done in a (row, column) format. So something like matrix(2,3) will call an item at the position of row 2, column 3. Matlab also always indexs from 1, not 0 like in many other languages out there.
If you have a single row or a single column (commonly referred to as a vector) then you simply call matrix(4) and that returns the 4th element. You can also have 3 or more layers to a matrix if you so desire. Think a matrix of matrices if you want.
Cells are extremely useful when it comes to storing variable length data in a single location. When data is stored in a cell it is still called in the same manner as you would a matrix but you have to convert it from the cell type to a matrix (cell2mat) for some uses. You'll learn those pretty quick. There's other ways to convert from cell as well, such as cell2num.
Hope that helps some more!
I have a structure in MATLAB. When I try to access a field, I see this displayed:
[4158x5 double]
How do I get the array itself?
My guess is that the matrix stored in your structure field is encapsulated in a cell array, so you need to use curly braces {} to index the cell contents (i.e. content indexing). Consider this example:
>> S.field1 = {1:5}; %# Create structure S with field 'field1' containing a cell
%# array which itself contains a 1-by-5 vector
>> S.field1 %# Index just the field...
ans =
[1x5 double] %# ...and you see the sort of answer you were getting
>> S.field1{1} %# Index the field and remove the contents of the cell...
ans =
1 2 3 4 5 %# ...and now you get the vector
NOTE: In newer versions of MATLAB things are displayed a bit differently, which avoids this confusion. Here's what you would see now:
>> S.field1
ans =
cell % Note now that it displays the type of data
[1×5 double]