Take an example,
a = struct('in',1,'out',2)
b = struct('temperature',6,'light',5,'output',2)
How do I get the last field and value that I input?
To get the last field of a,
z = a.out
To get the last field of b,
x = b.output
Or if you don't know what the field names are you can find them in the following way:
names = fieldnames(a)
I hope that helps.
The documentation for a struct says:
The most common way to access the data
in a structure is by specifying the
name of the field that you want to
reference.
In contrast to an array, where elements are accessed by index -> position, a struct field is accessed by the fieldname -> name.
See How do I access MATLAB structure fields within a loop? on how to iterate over all all fields of a struct.
Related
I have large data sets which i want to work with in matlab.
I have a struct called Trail containing serveral structures called trail1, trail2 ...
which then contain several matrices. I now want to add another point to for instance trail1
I can do that with Trail.trail1.a2rotated(i,:) = rotpoint'; the problem is that i have to do it in a loop where the trail number as well as the a2rotated changes to e.g. a3rot...
I tired to do it like that
name ="trail"+num2str(z)+".a2rotated"+"("+i+",:)";
name = convertStringsToChars(name);
Trail.(name) = rotpoint'
But that gives me the error: Invalid field name: 'trail1.a2rotated(1,:)'.
Does someone have a solution?
The name in between brackets after the dot must be the name of a field of the struct. Other indexing operations must be done separately:
Trail.("trail"+z).a2rotated(i,:)
But you might be better off making trail(z) an array instead of separate fields with a number in the name.
I have a struct x, with dynamic Fields, respectively dynamic Field names. But basically, only the first Field is relevant for me.
So I want to check if the Value of the first Field is empty, speak a 1x1cell or a 0x1cell..
or
I'm experimenting e.g. with:
isempty(fieldnames(x))
isempty(x(1))
if isempty(x(1))
msgbox('empty')
else
msgbox('result')
end
but got to no solution. Does anybody have a clue?
Speak, check if the Value of the first Field of the struct is empty or not..
If only the first field is relevant to you, then you can proceed as follows :
Get the fieldnames list of your struct
names=fieldnames(x);
Get the size of the first field
SizeOfFirstField=size(x.(names{1}));
Then you can just check if the first value in SizeOfFirstField is 0 or 1 in your if condition :
if SizeOfFirstField(1)==0
msgbox('empty')
else
msgbox('result')
end
Maybe you can also try this shorter form:
isempty(fieldnames(x))
where x is your struct variable.
Let me describe the question in this way. I have a .mat file, and if I open it, it contains a 1x10 struct data. In each data, it has a 1x5 struct (or field) called res. In res, it has a 1x1 struct (or field) called, let's say, foo. Thus, I have ixj copies of data(i).res(j).foo .
Is there anyway I can change the name of this foo? say I want all data(i).res(j).foo to become data(i).res(j).bar
I did search on the internet, and tried a few ways (add field and delete, create a temp field, use cell2field or fieldtofile, etc.) and all of them didn't work. The most frequent returned error is "Subscripted Assignment between dissimilar structures."
Please help, thanks in advance!
The safest way is probably by looping over data twice, the first pass creating a new field bar for each subfield like data(i).res(j).bar=data(i).res(j).foo, then the second pass deletes the old fields like data(i).res(j) = rmfield(data(i).res(j),'foo').
Thanks caoy and NotLikeThat. I finally came to an conclusion.
data2 = data
for i=1:10
for j = 1:5
data(i).res(j).bar = data2(i).res(j).foo;
end
data(i).res = rmfield(data(i).res, 'foo');
end
I probably need to removed i, j, and data2 after running this script.
I want to create a structure with a variable name in a matlab script. The idea is to extract a part of an input string filled by the user and to create a structure with this name. For example:
CompleteCaseName = input('s');
USER WRITES '2013-06-12_test001_blabla';
CompleteCaseName = '2013-06-12_test001_blabla'
casename(12:18) = struct('x','y','z');
In this example, casename(12:18) gives me the result test001.
I would like to do this to allow me to compare easily two cases by importing the results of each case successively. So I could write, for instance :
plot(test001.x,test001.y,test002.x,test002.y);
The problem is that the line casename(12:18) = struct('x','y','z'); is invalid for Matlab because it makes me change a string to a struct. All the examples I find with struct are based on a definition like
S = struct('x','y','z');
And I can't find a way to make a dynamical name for S based on a string.
I hope someone understood what I write :) I checked on the FAQ and with Google but I wasn't able to find the same problem.
Use a structure with a dynamic field name.
For example,
mydata.(casename(12:18)) = struct;
will give you a struct mydata with a field test001.
You can then later add your x, y, z fields to this.
You can use the fields later either by mydata.test001.x, or by mydata.(casename(12:18)).x.
If at all possible, try to stay away from using eval, as another answer suggests. It makes things very difficult to debug, and the example given there, which directly evals user input:
eval('%s = struct(''x'',''y'',''z'');',casename(12:18));
is even a security risk - what happens if the user types in a string where the selected characters are system(''rm -r /''); a? Something bad, that's what.
As I already commented, the best case scenario is when all your x and y vectors have same length. In this case you can store all data from the different files into 2 matrices and call plot(x,y) to plot each column as a series.
Alternatively, you can use a cell array such that:
c = cell(2,nufiles);
for ii = 1:numfiles
c{1,ii} = import x data from file ii
c{2,ii} = import y data from file ii
end
plot(c{:})
A structure, on the other hand
s.('test001').x = ...
s.('test001').y = ...
Use eval:
eval(sprintf('%s = struct(''x'',''y'',''z'');',casename(12:18)));
Edit: apologies, forgot the sprintf.
I am currently successfully using a CASE expression to update an empty column based on attributes from other columns. For example
UPDATE table SET cat = CASE
WHEN term = '{"Boulder"}' then 'Boulder'
However, I need to do the same but on an text array and particularly when an element is in a specific position within that array.
For example if the data looks like
{"Boulder, Tree, Bush"}
WHEN position('Tree' in term) > 0 then 'Boulder'
But I receive an error message
function pg_catalog.position(character varying[], unknown) does not exist
I have used position in a function before so I am not sure why PostgreSQL does not like it in this situation.
Is there a way to using a CASE expression whilst determining the position of a text element within an array.
Apparently your term column is defined as an array, e.g. varchar[]. The position function only works with scalar values, not with arrays.
If you want to test if an element is contained in an array you need to use a different operator: #>
update foobar
set cat = 'Boulder'
where term #> '{"Boulder"}'
The expression '{"Boulder"}' creates an array with a single element. It's equivalent to array['Boulder'] (which I find more readable). So the above where condition updates all rows where the array term contains all elements of the array on the right hand side of the operator. In this case it's only a single element you are testing for.
More details about the array functions and operators can be found in the manual: http://www.postgresql.org/docs/current/static/functions-array.html
Edit after the requirements have changed
To find and update only those where boulder is in the first, second or third place, you can use this:
update foobar
set cat = 'Boulder'
where 'Boulder' in (term[1], term[2], term[3]);