counting the number of data in the csv file
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Hello MATLAB community
temps is a bunch of numbers ranging from 20 to 70 in a column. So what I am struggling to do is that I want to sum the number of data points that are below 32 (just the number of data points not the actual data, which are numbers ranging from 20 to 70, summed up). Below is my code and I just don't know how to continue.
temps = load('40819DecJanLancasterTemp.csv');
plot(temps)
xlabel('Dec2018 Jan2018 Dec2019 Jan2019')
ylabel('Temperature (F)')
title('Hourly Temperature')
for i = 1:length(temps)
if temps(i) <= 32
elseif temps(i) > 32
end
end
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Image Analyst
2020-3-16
Try this
indexesBelow32 = temps < 32
countBelow32 = sum(indexesBelow32)
You could of course do it all in one shot:
countBelow32 = sum(temps < 32)
No for loop needed to do the count.
2 个评论
Image Analyst
2020-3-16
Yes, the trick is to understand the difference between logical indexes and linear indexes.
Logical indexes are either true or false (1 or 0) if the condition is met. So we can just sum those to get a count.
Linear indexes are the actual indexes, like 1,2,3,etc. So like if we had
temps = [1,99, 2, 88, 3, 77]
logicalIndexes = temps < 32
then logicalIndexes would be [1, 0, 1, 0, 1, 0]. If we sum that we get 3.
Now the linear indexes
linearIndexes = find(logicalIndexes) % Or, equivalently find(temps < 32)
would be [1, 3, 5], which is a list of only where the logical indexes are "true" (meaning they're 1).
To get the actual numbers from the array, rather than their indexes/locations, you can use either the logical or linear indexes.
smallNumbers = temps(logicalIndexes)
smallNumbers = temps(linearIndexes)
smallNumbers would be [1,2,3] no matter which line of code above that you used. This is one of the wonderful things about a vectorized language like MATLAB.
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