My array contains a string in the first row
how can I sum the array from the 2nd row to the Nth/1442th row (as in my example) disregarding the negative signs present in the column?
for example, my code for an array called data2 is:
S = sum(data2(2,15):data2(1442,15));
so sum all of the elements from row 2 to row 1442 in column 15.
This doesn't work but it also does not have anything to deal with the absolute value of whatever row its checking
data is from a .csv:
You should do something like this:
sum(abs(data(2:1442,15)));
The abs function will find the absolute value of each value in the array (i.e. disregard the negative sign). data(2:1442,15) will grab rows 2-1442 of the 15th column, as you wanted.
EDIT: apparently data is a cell array, so you could do the following, I think:
sum(abs([data{2:1442,15}]));
Ok so it looks like you have a constant column so
data2(2,15) = -0.02
and further down
data2(1442,15) = -0.02 %(I would assume)
So when you form:
data2(2,15):data2(1442,15)
this is essential like trying to create an array but of a single value since:
-0.02:-0.02
ans =
-0.0200
which of course gives:
>> sum(-0.02:-0.02)
ans =
-0.0200
What you want should be more like:
sum(data2(2:1442,15))
That way, the index: 2:1442, forms a vector of all the row references for you.
To disregard the negative values:
your answer = sum(abs(data2(2:1442,15)))
EDIT: For a cell array this works:
sum(abs(cell2mat(data2(2:1442,15))))
Related
I have a column matrix and a cell array which has two columns.The first column has 1x2 doubles and the second column has 1x1 doubles.
For example
columnMatrix = [1;5];
cellArray = {[1,8],[10];[8,1],[20];[4,6],[80];[3,5],[40];[14,16],[85];[5,10],[36]};
I would like to search each element of columnMatrix in cellArray(:,1) and then return its corresponding value in cellArray(:,2)
For example the output has to be like this
newCell = {[1],[10,20];[5],[40,36]};
I tried using the ismember function in this way
[~,idx] = ismember(cell2mat(cellArray(:,1)),columnMatrix (: , 1));
This returns all the indices which have the searched element but they are in two seperate columns and I can not perform any other logical operation to get the corresponding second column entry.
Is there some way this operation can be achieved? Could some one please help?
Thanks
First of all, convert first column of cellArray to a matrix so it would be easier to search values in. Then iterate over columnMatrix values (e.g. using arrayfun, but you could also use for loop), find rows that match (any across columns) and select corresponding values from the second column of cellArray, converting to numeric array ([cellArray{...,2}]). Finally, append the columnMatrix as the first column of the resulting cell array:
columnMatrix = [1;5]; cellArray = {[1,8],[10];[8,1],[20];[4,6],[80];[3,5],[40];[14,16],[85];[5,10],[36]};
mat = cell2mat(cellArray(:,1));
values = arrayfun(#(x) [cellArray{any(mat==x,2),2}], columnMatrix, 'uni', false);
result = [num2cell(columnMatrix), values];
I have a cell array that I need to split into several matrices so that I can take the sum of subsets of the data. This is a sample of what I have:
A = {'M00.300', '1644.07';...
'M00.300', '9745.42'; ...
'M00.300', '2232.88'; ...
'M00.600', '13180.82'; ...
'M00.600', '2755.19'; ...
'M00.600', '15800.38'; ...
'M00.900', '18088.11'; ...
'M00.900', '1666.61'};
I want the sum of the second columns for each of 'M00.300', 'M00.600', and 'M00.900'. For example, to correspond to 'M00.300' I would want 1644.07 + 9745.42 + 2232.88.
I don't want to just hard code it because each data set is different, so I need the code to work for different size cell arrays.
I'm not sure of the best way to do this, I was going to begin by looping through A and comparing the strings in the first column and creating matrices within that loop, but that sounded messy and not efficient.
Is there a simpler way to do this?
Classic use of accumarray. You would use the first column as an index and the second column as the values associated with each index. accumarray works where you group values that belong to the same index together and you apply a function to those values. In your case, you'd use the default behaviour and sum things together.
However, you'll need to convert the first column into numeric labels. The third output of unique will help you do this. You'll also need to convert the second column into a numeric array and so str2double is a perfect way to do this.
Without further ado:
[val,~,id] = unique(A(:,1)); %// Get unique values and indices
out = accumarray(id, str2double(A(:,2))); %// Aggregate the groups and sum
format long g; %// For better display of precision
T = table(val, out) %// Display on a nice table
I get this:
>> T = table(val, out)
T =
val out
_________ ________
'M00.300' 13622.37
'M00.600' 31736.39
'M00.900' 19754.72
The above uses the table class that is available from R2013b and onwards. If you don't have this, you can perhaps use a for loop and print out each cell and value separately:
for idx = 1 : numel(out)
fprintf('%s: %f\n', val{idx}, out(idx));
end
We get:
M00.300: 13622.370000
M00.600: 31736.390000
M00.900: 19754.720000
I have the following cell array:
<20x2>
<32x2>
<28x2>
<30x2>
What I am trying to do is read into row 1 of the cell array which is <20x2> and once I am in <20x2> I would like to apply the following function to the first column only.
In the first one I would like every row of column 1 in C{1,1} to be subtracted by 0.1. In the second one C{2,1} (<32x2>) I would like every row of column 1 to be subtracted by 0.2 and so on...
So to clarify I am trying to subtract n*0.1 from the first column of each submatrix in the cell array where n= row number of the cell array. So if there was a section in the cell array in row 8, column 1 would be subtracted by 8*0.1 = 0.8
I hope the question is clear enough, I have tried to word it as clear as I can.
Thanks in advance for any help/suggestions
Attempt
First = C{1,1}(:,1);
Subtraction = First - 0.1
Gives me my desired result but only for row 1 of my cell array.
Unique question to Applying function to vectors row by row because this involves a cell array as opposed to a matrix. The aspect of reading into a cell array makes it a different variant of the problem so if somebody was having a similar problem to this question the mentioned 'duplicate' question would not help, especially with little MATLAB knowledge like myself
It is very easy to adapt your attempt to a loop:
for n = 1:size(c,1)
C{n,1}(:,1) = C{n,1}(:,1) - n*0.1;
end
I'm quite new to MatLab and this problem really drives me insane:
I have a huge array of 2 column and about 31,000 rows. One of the two columns depicts a spatial coordinate on a grid the other one a dependent parameter. What I want to do is the following:
I. I need to split the array into smaller parts defined by the spatial column; let's say the spatial coordinate are ranging from 0 to 500 - I now want arrays that give me the two column values for spatial coordinate 0-10, then 10-20 and so on. This would result in 50 arrays of unequal size that cover a spatial range from 0 to 500.
II. Secondly, I would need to calculate the average values of the resulting columns of every single array so that I obtain per array one 2-dimensional point.
III. Thirdly, I could plot these points and I would be super happy.
Sadly, I'm super confused since I miserably fail at step I. - Maybe there is even an easier way than to split the giant array in so many small arrays - who knows..
I would be really really happy for any suggestion.
Thank you,
Arne
First of all, since you wish a data structure of array of different size you will need to place them in a cell array so you could try something like this:
res = arrayfun(#(x)arr(arr(:,1)==x,:), unique(arr(:,1)), 'UniformOutput', 0);
The previous code return a cell array with the array splitted according its first column with #(x)arr(arr(:,1)==x,:) you are doing a function on x and arrayfun(function, ..., 'UniformOutput', 0) applies function to each element in the following arguments (taken a single value of each argument to evaluate the function) but you must notice that arr must be numeric so if not you should map your values to numeric values or use another way to select this values.
In the same way you could do
uo = 'UniformOutput';
res = arrayfun(#(x){arr(arr(:,1)==x,:), mean(arr(arr(:,1)==x,2))), unique(arr(:,1)), uo, 0);
You will probably want to flat the returning value, check the function cat, you could do:
res = cat(1,res{:})
Plot your data depends on their format, so I can't help if i don't know how the data are, but you could try to plot inside a loop over your 'res' variable or something similar.
Step I indeed comes with some difficulties. Once these are solved, I guess steps II and III can easily be solved. Let me make some suggestions for step I:
You first define the maximum value (maxValue = 500;) and the step size (stepSize = 10;). Now it is possible to iterate through all steps and create your new vectors.
for k=1:maxValue/stepSize
...
end
As every resulting array will have different dimensions, I suggest you save the vectors in a cell array:
Y = cell(maxValue/stepSize,1);
Use the find function to find the rows of the entries for each matrix. At each step k, the range of values of interest will be (k-1)*stepSize to k*stepSize.
row = find( (k-1)*stepSize <= X(:,1) & X(:,1) < k*stepSize );
You can now create the matrix for a stepk by
Y{k,1} = X(row,:);
Putting everything together you should be able to create the cell array Y containing your matrices and continue with the other tasks. You could also save the average of each value range in a second column of the cell array Y:
Y{k,2} = mean( Y{k,1}(:,2) );
I hope this helps you with your task. Note that these are only suggestions and there may be different (maybe more appropriate) ways to handle this.
I have a 60,000-by-2 array. The first column is data 1 and second column is data 2; both of equal length. I'm not sure how to properly write the syntax to compare data 1 to data 2, and if data 1 is larger than data 2 then write that to the third column. Or vice versa if data 2 is larger than data 1. I have begun constructing a for loop, but I'm having syntax issues comparing the columns.
No loops are needed. If you simply want to create a vector containing the largest element in each row of your 60,000-by-2 matrix you can use the max function:
A = rand(6e4,2); % Random demo data
B = max(A,[],2);
Or if you then want to put the result directly in a third column of A:
A(:,3) = max(A,[],2);
Read the documentation for max. You'll see that the 2 in the third argument applied the max function across each row of the input, A.