I want to load an ASCII-file using this syntax:
load('10-May-data.dat')
The returned output variable name should be X10_May_data.
Is there a way to get the variable name in Matlab? If I want to use regular expression to do the translation, how can I do it? For example, put an X before any underscores or digits in the filename and replace any other non-alphabetic characters with underscores.
The who function returns the names of variables in matlab. It also has a built-in regexp for selecting certain items:
X10_May_data = [1 2 3];
save X10_May_data.mat X10_May_data
clear
load X10_May_data.mat
w = who('-regexp','X*')
w =
'X10_May_data'
You can then operate on w{1} to do any substitutions you want. For example, use the strrep function for simple modifications of a string:
newvar = strrep(w{1},'May','latest')
newvar =
X10_latest_data
For more complex modifications, use regexp or regexprep. When you have the new name, you can assign it with eval:
eval([newvar '=' w{1}]) % like typing "X10_latest_data = X10_May_data"
X10_latest_data =
1 2 3
[edit] PS I agree with the comments that eval is usually a bad idea; but sometimes you just need to get something done :) For alternative approaches, see the matlab page on the topic.
Related
Context
I am designing a code that runs a bunch of calculations, and outputs figures. At the end of the code, I want to save everything in a nice way, so my take on this is to go to a user specified Output directory, create a new folder and then run the save process.
Question(s)
My question is twofold:
I want my folder name to be unique. I was thinking about getting the current date and time and creating a unique name from this and the input filename. This works but it generates folder names that are a bit cryptic. Is there some good practice / convention I have not heard of to do that?
When I get the datetime string (tn = datestr(now);), it looks like that:
tn =
'07-Jul-2022 09:28:54'
To convert it to a nice filename, i replace the '-',' ' and ':' characters by underscores and append it to a shorter version of the input filename chosen by the user. I do that using strrep:
tn = strrep(tn,'-','_');
tn = strrep(tn,' ','_');
tn = strrep(tn,':','_');
This is fine but it bugs me to have to use 3 lines of code to do so. Is there a nice one liner to do that? More generally, is there a way to look for every non letter or number character in a string and replace it with a given character? I bet that's what regexp is there for but frankly I can't quite get a hold on how regexps work.
Your point (1) is opinion based so you might get a variety of answers, but I think a common convention is to at least start the name with a reverse-order date string so that sorting alphabetically is the same as sorting chronologically (i.e. yymmddHHMMSS).
To answer your main question directly, you can use the built-in makeValidName utility which is designed for making valid variable names, but works for making similarly "plain" file names.
str = '07-Jul-2022 09:28:54';
str = matlab.lang.makeValidName(str)
% str = 'x07_Jul_202209_28_54'
Because a valid variable can't start with a number, it prefixes an x - you could avoid this by manually prefixing something more descriptive first.
This option is a bit more simple than working out the regex, although that would be another option which isn't too nasty here using regexprep and replacing non-alphanumeric chars with an underscore:
str = regexprep( str, '\W', '_' ); % \W (capital W) matches all non-alphanumeric chars
% str = '07_Jul_2022_09_28_54'
To answer indirectly with a different approach, a nice trick with datestr which gets around this issue and addresses point (1) in one hit is to use the following syntax:
str = datestr( now(), 30 );
% str = '20220707T094214'
The 30 input (from the docs) gives you an ISO standardised string to the nearest second in reverse-order:
'yyyymmddTHHMMSS' (ISO 8601)
(note the T in the middle isn't a placeholder for some time measurement, it remains a literal letter T to split the date and time parts).
I normally use your folder naming approach with a meaningful prefix, replacing ':' by something else:
folder_name = ['results_' strrep(datestr(now), ':', '.')];
As for your second question, you can use isstrprop:
folder_name(~isstrprop(folder_name, 'alphanum')) = '_';
Or if you want more control on the allowed characters you can use good old ismember:
folder_name(~ismember(folder_name, ['0':'9' 'a':'z' 'A':'Z'])) = '_';
I'm trying to export a matrix f that is double. My data in f are real numbers in three columns. I want a txt file as an output with the columns separated by tabs. However, when I try the dlmwrite function, just the first column appears as output.
for k = 1:10
f = [idx', firsttime', sectime'];
filename = strcat(('/User/Detection_rerun/AF_TIMIT/1_state/mergedlabels_train/'),(files_train{k,1}),'.lab');
dlmwrite(filename,f,'\t') ;
end
When I use dlmwrite(filename,f,'\t','newline','pc') ; I keep getting an error Invalid attribute tag: \t . I even tried 'tab' instead of '\t' but a similar error appears. Please let me know if you have any suggestions. thank you
This is because you are not calling dlmwrite properly. To specify the delimiter, you must use the delimiter flag, followed by the specific delimiter you want. In your case, you use \t. In other words, you need to do this:
for k = 1:10
f = [idx', firsttime', sectime'];
filename = strcat(('/User/Detection_rerun/AF_TIMIT/1_state/mergedlabels_train/'),(files_train{k,1}),'.lab');
dlmwrite(filename,f,'delimiter','\t') ;
end
BTW, you are using the newline flag with pc, meaning that you are specifying carriage returns that are recognized by a PC. I suggest you leave this out and allow MATLAB to automatically infer this. Only force the newline characters if you know what you're doing.
FWIW, the MATLAB documentation is pretty clear about delimiters and other quirks about the function: http://www.mathworks.com/help/matlab/ref/dlmwrite.html
In a matlab program I have an external parameter file that needs to be read in. Like
a = 1/3
b = 'test'
Currently I use textscan to read this file and use str2num to parse the values of a. However, I read that str2num use eval inside, which is undesirable for safety reason: what if someone made a = 'delete something', and then str2num will execute the string as a side effect. str2double does not work for fractional numbers. Is there any better way to parse 1/3 from external file into matlab?
If you are going to parse input that can only be a simple number or a division, the str2double/str2double approach may be sufficient. However if you want to parse input safely in general, I would recommend restricting the input.
For example like so:
rawString= 'dir+3/5'
safeCharacters = ['0':'9' '+-*/\^eEij. '];
if all(ismember(rawString,safeCharacters))
str2num(junkString)
end
Of course this may filter out some potentially good input like: str2num('rand')
Personally, I'd use str2num (which is based on eval if you read the documentation). However, another option is sym. The Symbolic Math toolbox is based on eval as well of course, but it has input validation to avoid the potential dangers you're worried about. It is very robust and simple to use for what you need:
a = '1/3';
a = double(sym(a))
This also handles converting cell arrays of strings to vectors and matrices gracefully:
a={'1/3','1/33','1/333'; ...
'2/3','2/33','2/333'};
a = double(sym(a))
The following unlikely input will return warnings and an error (and not delete a in memory):
b = 'delete a';
a = double(sym(b))
Thus you may want to use a try/catch statement to gracefully handle cases when a user may provide invalid input:
try
Xs = double(sym(X));
catch err
if strcmp(err.id,'MATLAB:UndefinedFunction')
error('YourFunctionName:UnknownInput','Your helpful message here.');
else
rethrow(err);
end
end
You could equally replace the Xs = double(sym(X)); line with a call to str2num.
You can explicitly search for the backslash with strfind.
if ~isempty(strfind(X, '/'))
% then use str2num
else
% use str2double, and if this returns a NaN, then it is a string
end
Or use strtok to split the string using '/' as a token, and use str2double on all resulting elements.
I'm going to read some function from a Unicode text file in matlab and calculate there answer with my own variables. first i use fopen to read the text file, then what should i do to convert each line of that text file to a function? for example the func.txt contains:
(x^2)-3y
sin(x+z)+(y^6)
and i need to write an m.file which read func.txt and process that like this:
function func1[x,y] = (x^2)-3y
function func2[x,y,z] = sin(x+z)+(y^6)
Preamble: if your final aim is to use those functions in matlab (i.e. evaluate them for some values of x,y,...), I would rather suggest the following approach that looks more robust to me.
In principle, in fact, you don't need to manipulate the file funct.txt to evaluate the functions defined therein.
First problem: each line of your file funct.txt must define an inline function.
Say that the first function (i.e., the first line) of the file funct.txt has been copied into a string str,
str = '(x^2)-3y',
you can obtain a function from it using the command inline:
f1 = inline(str,'x','y');
which gives to you (matlab output)
f1 =
Inline function:
f1(x,y) = (x^2)-3y.
Now you can use f1 just calling it as f1(x,y), for whatever values x,y.
Second problem: you have to parse your file funct.txt to obtain the strings str containing the definitions of your functions. That's easier, you may want to consider the function fgets.
Third problem: the functions in funct.txt may depend on 2,3 (or more?) independent variables. As far as I know there is no easy way to parse the string to discover it. Thus, you may want to define each inline function as depending on all your independent variables, i.e.
f1 = inline('(x^2)-3y','x','y','z');
the variable z will play no active role, by the way. Nonetheless, you need to specify a third dummy parameter when you call f1.
How to use matlab regexprep , for multiple expression and replacements?
file='http:xxx/sys/tags/Rel/total';
I want to replace 'sys' with sys1 and 'total' with 'total1'. For a single expression a replacement it works like this:
strrep(file,'sys', 'sys1')
and want to have like
strrep(file,'sys','sys1','total','total1') .
I know this doesn't work for strrep
Why not just issue the command twice?
file = 'http:xxx/sys/tags/Rel/total';
file = strrep(file,'sys','sys1')
strrep(file,'total','total1')
To solve it you need substitute functionality with regex, try to find in matlab's regexes something similar to this in php:
$string = 'http:xxx/sys/tags/Rel/total';
preg_replace('/http:(.*?)\//', 'http:${1}1/', $string);
${1} means 1st match group, that is what in parenthesis, (.*?).
http:(.*?)\/ - match pattern
http:${1}1/ - replace pattern with second 1 as you wish to add (first 1 is a group number)
http:xxx/sys/tags/Rel/total - input string
The secret is that whatever is matched by (.*?) (whether xxx or yyyy or 1234) will be inserted instead of ${1} in replace pattern, and then replace instead of old stuff into the input string. Welcome to see more examples on substitute functionality in php.
As documented in the help page for regexprep, you can specify pairs of patterns and replacements like this:
file='http:xxx/sys/tags/Rel/total';
regexprep(file, {'sys' 'total'}, {'sys1' 'total1'})
ans =
http:xxx/sys1/tags/Rel/total1
It is even possible to use tokens, should you be able to define a match pattern for everything you want to replace:
regexprep(file, '/([st][yo][^/$]*)', '/$11')
ans =
http:xxx/sys1/tags/Rel/total1
However, care must be taken with the first approach under certain circumstances, because MATLAB replaces the pairs one after another. That is to say if, say, the first pattern matches a string and replaces it with something that is subsequently matched by a later pattern, then that will also be replaced by the later replacement, even though it might not have matched the later pattern in the original string.
Example:
regexprep('This\is{not}LaTeX.', {'\\' '([{}])'}, {'\\textbackslash{}' '\\$1'})
ans =
This\textbackslash\{\}is\{not\}LaTeX.
=> This\{}is{not}LaTeX.
and
regexprep('This\is{not}LaTeX.', {'([{}])' '\\'}, {'\\$1' '\\textbackslash{}'})
ans =
This\textbackslash{}is\textbackslash{}{not\textbackslash{}}LaTeX.
=> This\is\not\LaTeX.
Both results are unintended, and there seems to be no way around this with consecutive replacements instead of simultaneous ones.