I am trying to extract the coordinates located in the variable x within a .mat structure. I would like to print them as a three column matrix. Let's say:
-5543837.67700032 -2054567.16633347 2387852.25825667
4641938.565315761 393003.28157792 4133325.70392322
-3957408.7414133 3310229.46968631 3737494.72491701
1492206.38965564 -4458130.51073730 4296015.51539152
4075539.69798060 931735.497964395 4801629.46009471
3451207.69353006 3060375.44622100 4391915.05780934
I know that I can get them with
file=load('./filee_scan.mat')
stat = [file.scan.stat]';
x = [stat.x]';
But I get something like:
-5543837.67700032
-2054567.16633347
2387852.25825667
4641938.565315761
393003.28157792
4133325.70392322
% :: and so on
I would like to print them as I showed at the beginning (x as a vector of 3 coordinates and one line per station) but I don't know how to treat them. I have tried with loops but I really don't know how to express them.
How can I display my coordinates as an n -by- 3 matrix?
This is the scan file:
This is x:
[stat.x].' gives you a flattened vector, as you've seen. You can reshape() that vector to the desired format:
x = reshape(x,3,[]).';
This reshapes first to 3 rows and n columns (your number of stations), then transposed to have n rows of 3 columns.
For a short introduction on how reshape works, see this answer of mine.
Related
I'm trying to create a list of 50 random numbers let's say between 100 and 500 with one formula in Gsheets. Is there any formula like 'apply this to x cells'?
What I tried so far is (and doesn't work). I hoped randarray function will 'force' randbetween function to create 2D array (randarray creates a list of numbers between 0 and 1).
={
RANDARRAY(50,1), ARRAY_CONSTRAIN(RANDBETWEEN(100,500),50,1)
}
Error
Function ARRAY_ROW parameter 2 has mismatched row size. Expected: 50. Actual: 1.
So this error indicates that array_constrain didn't help either.
try like this:
=ARRAYFORMULA(RANDBETWEEN(ROW(A100:A149), 500))
In generic terms, if you need N random numbers, between X and Y, you would combine the following formulas:
RandBetween(X, Y)
Row(cell_ref)
Indirect(string_cell_ref)
ArrayFormula(array_formula)
Details
When combining a Row(cell_ref) with an ArrayFormula, you can specify a cell range or simply a number range:
ArrayFormula(Row(1:50))
The above example generates a one dimensional array (column) with the numbers 1 through 50. In order to programmatically change the number, we use the Indirect function to specify the upper bound of the range, N:
ArrayFormula(Row(Indirect("1:"&N)))
N can be a named range, hard coded, or a cell reference containing a number greater than 0. Because you want each row to contain a random number between X and Y, you need to eliminate the sequential number in each array position by multiplying the number generated by the above formula by zero:
ArrayFormula(Row(Indirect("1:"&N))*0)
which generates a on dimensional array (column) of N zeros. Now you can combine this as follows to generate a one dimensional array (column) of N random numbers between X and Y:
Solution
ArrayFormula(RandBetween(Row(Indirect("1:"&N))*0+X, Y))
You could use named ranges for N, X, and Y; hard code them eg. 50, 100, 500; or use simple cell references as in the example below:
ArrayFormula(RandBetween(row(indirect("1:"&B1))*0+B2, B3))
GSheet Example
I have the following cell matrix, which will be used as a confusion matrix:
confusion=cell(25,25);
Then, I have two other cell arrays, on which each line contains predicted labels (array output) and another cell matrix containing the real labels (array groundtruth).
whos output
Name Size Bytes Class Attributes
output 702250x1 80943902 cell
whos groundtruth
Name Size Bytes Class Attributes
groundtruth 702250x1 84270000 cell
Then, I created the following script to create the confusion matrix
function confusion=write_confusion_matrix(predict, groundtruth)
confusion=cell(25,25);
for i=1:size(predict,1)
confusion{groundtruth{i},predict{i}}=confusion{groundtruth{i}, predict{i}}+1;
end
end
But when I run it in matlab I have the following error:
Index exceeds matrix dimensions.
Error in write_confusion_matrix (line 4)
confusion{groundtruth{i},predict{i}}=confusion{groundtruth{i}, predict{i}}+1;
I was curious to print output's and groundtruth's values to see what was happening
output{1}
ans =
2
groundtruth{1}
ans =
1
So, nothing seems to be wrong with the values, so what is wrong here? is the confusion matrix's indexing right in the code?
The error occurs in a for loop. Checking the first iteration of the loop is not sufficient in this case. Index exceeds matrix dimensions means there exists an i in the range of 1:size(output,1) for which either groundtruth{i} or output{i} is greater than 25.
You can find out which one has at least one element bigger than the range:
% 0 means no, there is none above 25. 1 means yes, there exists at least one:
hasoutlier = any(cellfun(#(x) x > 25, groundtruth)) % similar for 'output'
Or you can count them:
outliercount = sum(cellfun(#(x) x > 25, groundtruth))
Maybe you also want to find these elements:
outlierindex = find(cellfun(#(x) x > 25, groundtruth))
By the way, I am wondering why are you working with cell arrays in this case? Why not numeric arrays?
Let's say we have an array x. We can find the maximum value of this array as follows:
maximum = max(x);
If I have two arrays, let's say x and y, I can find the array that contains the maximum value by using the command
maximum_array = max(x, y);
Let's say that this array is y. Then, I can find the maximum value by using the max command with argument y, as before with x:
maximum_value = max(y);
This two-step procedure could be performed with the following compact, one-liner command:
maximum_value = max(max(x, y));
But what happens when we have more than 2 arrays? As far as I know, the max function does not allow to compare more than two arrays. Therefore, I have to use max for pairs of arrays, and then find the max among the intermediate results (which involves also the use of additional variables). Of course, if I have, let's say, 50 arrays, this would be - and it really is - a tedius process.
Is there a more efficient approach?
Approach #1
Concatenate column vector versions of them along dim-2 with cat and then use maximium values with max along dim-2 to get the max.
Thus, assuming x, y and z to be the input arrays, do something like this -
%// Reshape all arrays to column vectors with (:) and then use cat
M = cat(2,x(:),y(:),z(:))
%// Use max along dim-2 with `max(..,[],2)` to get column vector
%// version and then reshape back to the shape of input arrays
max_array = reshape(max(M,[],2),size(x))
Approach #2
You can use ndims to find the number of dimensions in the input arrays and then concatenate along the dimension that is plus 1 of that dimension and finally find max along it to get the maximum values array. This would avoid all of that reshaping back and forth and thus could be more efficient and a more compact code as well -
ndimsp1 = ndims(x)+1 %// no. of dimensions plus 1
maxarr = max(cat(ndimsp1,x,y,z),[],ndimsp1) %// concatenate and find max
I think the easiest approach for a small set of arrays is to column-ify and concatenate:
maxValue = max([x(:);y(:)]);
For a large number of arrays in some data structure (e.g. a cell array or a struct), I simple loop would be best:
maxValue = max(cellOfMats{1}(:));
for k = 2:length(cellOfMats)
maxValue = max([maxValue;cellOfMats{k}(:)]);
end
For the pathological case of a large number of separate arrays with differing names, I say "don't do that" and put them in a data structure or use eval with a loop.
I have an 1000 element array with values ranging from 1 - 120. I want to split this array into 6 different subarrays with respect to the value range
for ex:
array1 with values from ranges 0-20.
array 2 with values from range 20-40........100-120 etc.
At the end I would like to plot a histogram with X-axis as the range and each bar depicting the number of elements in that range. I dont know of any other way for 'this' kind of plotting.
Thanks
In other words, you want to create a histogram. Matlab's hist() will do this for you.
If you only need the histogram, you can achieve the result using histc, like this:
edges = 0:20:120; % edges to compute histogram
n = histc(array,edges);
n = n(1:end-1); % remove last (no needed in your case; see "histc" doc)
bar(edges(1:end-1)+diff(edges)/2, n); % do the plot. For x axis use
% mean value of each bin
I am new to Matlab.
Lets say I have an array a = [1:1:1000]
I have to divide this into 50 parts 1-20; 21-40 .... 981-1000.
I am trying to do it this way.
E=1000X
a=[1:E]
n=50
d=E/n
b=[]
for i=0:n
b(i)=a[i:d]
end
But I am unable to get the result.
And the second part I am working on is, depending on another result, say if my answer is 3, the first split array should have a counter and that should be +1, if the answer is 45 the 3rd split array's counter should be +1 and so on and in the end I have to make a histogram of all the counters.
You can do all of this with one function: histc. In your situation:
X = (1:1:1000)';
Edges = (1:20:1000)';
Count = histc(X, Edges);
Essentially, Count contains the number of elements in X that fall into the categories defined in Edges, where Edges is a monotonically increasing vector whose elements define the boundaries of sequential categories. A more common example might be to construct X using a probability density, say, the uniform distribution, eg:
X = 1000 * rand(1000, 1);
Play around with specifications for X and Edges and you should get the idea. If you want the actual histogram plot, look into the hist function.
As for the second part of your question, I'm not really sure what you're asking.