I am trying to run a loop over multiple files, by feeding the file names into a function. I have saved these file names as a structure using:
files=dir('testdata\*.siz');
nrows=size(files,1);
Now my loop is:
for i=1:nrows
filename=files.name{i};
Singapore(filename);
writetable(ans,'file.xls')
end
However, I get the error:
"Field reference for multiple structure elements that is followed by more reference blocks is an error."
I found that the error is in
filename=files.name{1};
but everywhere I've searched tells me to use { } to access fields in a structure. I also have tried other types of brackets in vain.
Additional Information:
'files' is the name of the structure
'name' is the first column field within 'files' containing the file names in inverted commas.
You are referencing the files struct wrong, you need:
files(i).name
The {} is for accessing cell arrays.
You should also use ii (or similar) instead of i as your indexing variable since i is a already Matlab variable (imaginary unit).
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 small utility that checks for new columns for an intraday hdb and adds new columns.
At the moment I am using :
.[set;(pth;?[data;();();cls]);{[p;e] .log.error[.z.h;"Failed to save to path [",string[p],"] with error :",e]}[pth;]]
where path is :
`:path_to_hdb/2022.03.31/table01/newDummyThree
and
?[data;();();cls] // just an exec statement
Would it make any difference to use save instead:
.[save;(pth;?[data;();();cls]);{[p;e] .log.error[.z.h;"Failed to save to path [",string[p],"] with error :",e]}[pth;]]
Yes. If you are adding entire columns to a table then you might want to store it splayed, i.e. as a directory of column files rather than as a single table file. This means using set rather than save.
https://code.kx.com/q/kb/splayed-tables/
But test actual example updates.
As mentioned in the documentation for save:
Use set instead to save
a variable to a file of a different name
local data
So set has the advantage of not requiring a global and you can name the file a different name to the name of your in-memory global variable.
There is no difference in how they serialise/write the data. In fact, save uses set under the covers anyway:
q)save
k){$[1=#p:`\:*|`\:x:-1!x;set[x;. *p]; x 0:.h.tx[p 1]#.*p]}'
By the way - you can't use save in the way that you've suggested in your post. save takes a symbol as input and this symbol is the symbol name of your global variable containing the data you want to write.
I'm relatively new to matlab and would really appreciate any help.
Currently, I have a function (we'll call it readf) that reads in data from a single ascii file into a struct of multiple fields (we'll call it cdata).
names = cellstr(char('A','B','C','D','E','F','G'));
cdata = readf('filestring','dataNames',names);
The function works fine and gives me the correct output of a struct with these field names, with the value of each field name being a cell array of the corresponding data.
My task is to create a for loop that uses this readf function to read in a folder of these ascii files at once. I'm trying to work it so that the for loop creates a struct with an index of the different cdata structs. After trying a few different methods, I am stumped.
This is what I have so far.
files = struct2cell(dir('folderstring')); %creates a cell array of the names of the files withing the folder
for ii=length(files);
cdata(ii) = readf([folderstring,files(1,1:ii),names],'dataName',names);
end;
This is currently giving me the following error.
"Error using horzcat
Dimensions of matrices being concatenated are not consistent."
I am not sure what is wrong. How can I fix this code so i can read in all the data from a folder at once??? Is there a better and more efficient way to do this than making an index to this struct? Perhaps a cell array of different structures or even a structure of nested structures? Thanks!
Change:
for ii=length(files);
cdata(ii) = readf([folderstring,files(1,1:ii),names],'dataName',names);
end;
To:
for ii=1:length(files); % CHECK to make sure length(files) is giving you the right number
cdata(ii) = readf([folderstring,files{ii},names],'dataName',names);
end;
% CHECK files{ii}, with 1,2,3 etc. is giving you the correct file name.
I'm building a facial recognition program and loading a whole bunch of images which will be used for training.
Currently, I'm reading my images in using double loops, iterating through subfolders in a folder.
Is there any way, as it iterates, that the images file name can be used before the image is read and stored?
eg. I have an image person001.jpg. How can you retrieve that name (person001) then read the image in like: person001 = imread('next iteration of loop which happens to be person001');
Thanks in advance.
I strongly recommend not to use unstructured variables. First it's very difficult to do operations like "iterate over all images", second you can get strange problems covering a function name with a variable name. Instead i would use a struct with dynamic field names or a map. A solution with a Map propably allows all possible file names.
Dynamic field names:
dirlisting=dir('.jpg');
for imageIX=1:numel(dirlisting)
%cut of extension:
[~,name,~]=fileparts(dirlisting(imageIX).name);
allImages.(name)=imread(dirlisting(imageIX).name);
end
You can access the images in a struct with allImages.person001 or allImages.(x)
Map:
allImages=containers.Map
dirlisting=dir('.jpg');
for imageIX=1:numel(dirlisting)
%cut of extension:
[~,name,~]=fileparts(dirlisting(imageIX).name);
allImages(name)=imread(dirlisting(imageIX).name);
end
You can access the images in a Map using allImages('person001'). Using a Map there is no need to cut of the file extension.
I am trying to reference an element buried within a structure that I did not create (hence I don't know the exact way in which it was built).
Having loaded the structure, if I type:
dataFile.RECORDINGS.eye
I receive the following output:
ans =
2
ans =
2
Both of those variables will always be the same, but they could be at any time 1, 2 or 3. What I'd like to do is check with a switch statement which looks like this:
switch dataFile.RECORDINGS.eye
case {1, 2}
% action A
case 3
% action B
end
Of course, the above throws up an error because 'case' cannot check whether dataFile.RECORDINGS.eye contains a given value since there are two elements stored under that address. So, my question is: how do I reference just one of the elements? I thought it would be as simple as replacing the first line with:
switch dataFile.RECORDINGS.eye(1)
...But, this gives the error:
??? Field reference for multiple structure elements that is followed by more reference blocks is an error.
Similarly, I can't access the element like this:
switch dataFile.RECORDINGS.eye.1
...As I get the following error:
??? Dot name reference on non-scalar structure.
If the values are really always the same, you can try the following to get a scalar that can be used in the switch command:
unique([dataFile.RECORDINGS.eye])
By the way, did you try to index RECORDINGS, i.e.,
dataFile.RECORDINGS(1).eye
dataFile.RECORDINGS(2).eye
Perhaps instead of eye having multiple elements, you have multiple elements of RECORDINGS that each have a single value of eye? You might want dataFile.RECORDINGS(1).eye or dataFile.RECORDINGS(2).eye.