How to replace NAN values in a string to a zero value
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Carolina Corella Velarde
on 19 Dec 2022
Hi I'm working with this text file and need to replace the "NAN" to a zero value
"Temperature","VW"
20.55,41.45
17.79,41.37
16.49,41.29
14.9,41.21
14.22,41.12
12.02,41.04
10.09,40.96,
9.47,"NAN"
8.623,"NAN"
6.855,"NAN"
6.197,40.57
17.08,40.49
14.19,40.42
17.66,40.38
I'm trying yo use for and if loops to remove and replace the NAN to a zero however after using the coded I have shared below, MATLAB is giving me this error:
Array indices must be positive integers or logical values.
Error in Replacing_NAN (line 11)
if VW(i)=='NAN'
Can anyone help me to see what I'm doing wrong please?
clear all
clc
fileID=fopen('F:\home\carolina\Met_files_code\Replacing_NAN_Test_File.txt','r');
data=textscan(fileID,' %f %s','HeaderLines', 1,'Delimiter', ',');
Temperature=data{1};
VW=data{2};
%remove NAN from the VW data column
n=length(VW)
for i=0,i<n
if VW(i)=='NAN'
'NAN'==0
end
end
disp(VW)
2 Comments
Accepted Answer
Image Analyst
on 19 Dec 2022
Try this:
m = readmatrix('Replacing_NAN_Test_File.txt')
Temperature = m(:, 1);
VW = m(:, 2);
% Replace nans with 0
VW(isnan(VW)) = 0
3 Comments
Walter Roberson
on 20 Dec 2022
But readmatrix() is converting the "NaN" character vectors to numeric nan.
More Answers (2)
Walter Roberson
on 19 Dec 2022
If you must use textscan() then skip most of that and use the TreatAsEmpty option; https://www.mathworks.com/help/matlab/ref/textscan.html#btghhyz-1-TreatAsEmpty
However I would suggest that you instead use readmatrix() with the TreatAsMissing option.
You need to decide what you want to do about the fact that the line
10.09,40.96,
has three variables instead of 2. The ExpectedNumVariables option might help; if not then if you use detectImportOptions you can set the number of variables in the options and you can set the rule to discard extra columns.
0 Comments
Bora Eryilmaz
on 19 Dec 2022
Edited: Bora Eryilmaz
on 19 Dec 2022
Your for-loop is not a valid MATLAB expression. It should probably be:
for i = 1:n
end
When i == 0, VW(i) would not be valid MATLAB indexing since arrays don't have 0th element.
Also, 'NAN'==0 will not replace VM(i) with 0. Instead, do something like this:
if isequal(VW(i), 'NAN')
VW(i) = 0;
end
5 Comments
Bora Eryilmaz
on 19 Dec 2022
Edited: Bora Eryilmaz
on 19 Dec 2022
It is not a "valid" expression considering what the OP is trying to do. A technically valid expression doing the wrong thing is not really a valid expression.
Walter Roberson
on 20 Dec 2022
You had written,
"Your for-loop is not a valid MATLAB expression."
But it is a valid MATLAB expression.
VW(1) = "NAN"
n = 2
for i=0,i<n
if VW(i+1)=='NAN'
'NAN'==0
end
end
MATLAB is willing to execute it, so it is a valid MATLAB expression. It just doesn't do what the user might hope.
valid, adjective:
(3) legally or officially acceptable.
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