Undefined function or variable 'isnan'
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I am met with the error "Undefined function or variable 'isnan'" when running this code:
%counter = 1:4
%a is a 220x4 cell
%data is a 220x4 double
for i = size(a, 1)
pairs = [];
pairs(:,1) = counter;
pairs(:,2) = data(i,:);
pairs = pairs(~isnan(pairs(:,2),:));
slope(i) = polyfit(pairs(:,1),pairs(:,2),1);
end
I can't seem to figure out exactly why. Is the way I'm using the NOT operator?
3 个评论
Stephan
2019-1-7
What is the result of:
which isnan -all
Carver Nabb
2019-1-7
nanren888
2019-1-7
As Walter says; It is complaining about the two-parameter isnan(x,y) that you've invented :)
采纳的回答
Walter Roberson
2019-1-7
You have
pairs = pairs(~isnan(pairs(:,2),:));
You want
pairs = pairs(~isnan(pairs(:,2)),:);
21 个评论
nanren888
2019-1-7
Yes, it is complaining about the two-parameter isnan(x,y) that you've invented :)
per isakson
2019-1-7
How difficult could it be to produce a better error message?
>> isnan( 17, : )
Undefined function or variable 'isnan'.
Carver Nabb
2019-1-7
Carver Nabb
2019-1-7
Walter Roberson
2019-1-7
It is an oddity of the parser, which has some messy behaviour for colon.
functionname(argument, :)
will disable recognition of functionname as a function and will look for a variable with that name, probably resulting in the misleading error message.
A = reshape(1:60, 2, []);
A(1:2)
%1:2 gets computed as [1 2] first, then the datatype of A is looked up
%and since it is a variable, subsref is invoked to select the first two elements
A('1:2')
%'1:2' is a vector of characters, equivalent to char([49 58 50]) .
%The numeric equivalent is taken, [49 58 50] and are used as subscripts into A
A(:)
%the : is transformed into subsref() with type '()' and index {':'}
%which is treated by subsref as a reshape request
A(':')
%the ':' with the character scalar ':' is transformed into subsref() with
% type '()' and index {':'} which is treated as a reshape request
A(1, :)
%this is transformed into subsref() with type '()' and index {1, ':'}
%which is treated by subsref as a subset indexing request
A(1, ':')
%this is transformed into subsref() with type '()' and index {1, ':'}
%which is treated by subsref as a subset indexing request
A(1, '1:2')
%this is transformed into subsref() with type '()' and index {1, '1:2'}
%which is treated by subsref as a subset indexing request with
%the '1:2' being treated as equivalent to [49 58 50]
but
functionname(argument, ':')
is not treated as a subsref request.
Walter Roberson
2019-1-7
polyfit() with third parameter N requests a fitting in which the maximum exponent used for the independent variable is N. Since exponents all the way down to 0 are used, that results in N+1 results. So when you requested polyfit(x,y,1) you are going to get out 1+1 = two coefficients, one for x^1 and one for x^0 (the constant term)
Carver Nabb
2019-1-7
Carver Nabb
2019-1-7
Walter Roberson
2019-1-7
For the isnan() matter, you just accidentally had the : inside the isnan function call and needed to move it outside that call into a place it was acting as a subscript.
polyfit(pairs(:,1),pairs(:,2),0)
is always exactly equal to mean(pairs(:,2)) even when the x are irregularly spaced. If you want only a single coefficient then there is no point using polyfit().
If you want to fit the data to a straight line then you would need to expect two coefficients as output, like
mc = polyfit(pairs(:,1),pairs(:,2),1);
slope(i) = mc(1);
Jan
2019-1-7
@Carver Nabb: Use:
pairs = pairs(~isnan(pairs(:,2)),:);
Again the debugger will help you to understand, what happens. dbstop if error, run the code again, and when it stops:
polyfit(pairs(:,1),pairs(:,2),1)
size(polyfit(pairs(:,1),pairs(:,2),1))
size(slope(i))
You cannot assign a vector to a scalar. I guess you want:
P = polyfit(pairs(:,1),pairs(:,2),1);
slope(i) = P(2);
Carver Nabb
2019-1-7
Walter Roberson
2019-1-8
Question: why is your for loop to size(a,1) but you are not accessing a in the loop? It would look to me to make more sense to run to size(data,1)
Carver Nabb
2019-1-8
Walter Roberson
2019-1-8
Are you happening to see warnings such as
Warning: Polynomial is not unique; degree >= number of data points.
?
Carver Nabb
2019-1-8
Walter Roberson
2019-1-8
Can you attach a .mat with counter and data ?
Carver Nabb
2019-1-8
Carver Nabb
2019-1-8
Walter Roberson
2019-1-8
for i = size(allpcompst,1)
should be
for i = 1:size(allpcompst,1)
You will get messages Warning: Polynomial is not unique; degree >= number of data points. 207 of the 220 slopes are non-zero.
Carver Nabb
2019-1-8
Carver Nabb
2019-1-8
更多回答（2 个）
Jan
2019-1-7
Although I assume that Walter hit the point already, I suggest to use teh debugger to identify such problems. Type in the command window:
dbstop if error
Now run the code again until it stops. Check the currently processed line by evaluating it piecewise:
% pairs = pairs(~isnan(pairs(:,2),:))
pairs(:,2)
~isnan(pairs(:,2),:) % <- This should fail already
pairs(~isnan(pairs(:,2),:))
As Walter has said already, isnan(x, :) is meaningful only, if it is an array. Otehrwise using the colon as second input is not valid, if the function isnan() is meant. The error message "Undefined function or variable 'isnan'" is not really clear here. But splitting the commands into parts using the debugger helps to understand the problem.
Kholoud Alzoubi
2021-4-19
0 个投票
Undefined function or variable 'textdata'.
Error in KopackRFNNGOA (line 15)
x1=textdata(~isnan(textdata)); %temperature
1 个评论
Walter Roberson
2021-4-19
Not enough context.
You are trying to use a variable named textdata that has not been assigned to.
Also, the variable name would tend to suggest that the variable is not expected to hold numeric data, so isnan() is questionable here.
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