How can I convert a dataset of numbers into a dataset of logarithms of these numbers
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Hi
I have imported an Excel dataset of real-time GDP. Which is a dataset of numbers in a triangular format.
So I want to convert this dataset into logs of these numbers. Is there any fast way??
Many thanks
3 个评论
Star Strider
2014-7-2
What is a ‘triangular format’?
John D'Errico
2014-7-2
By using the log function?
Panty
2014-7-2
采纳的回答
Star Strider
2014-7-2
You need to load the dataset into the MATLAB workspace (use xlsread), then simply use the logarithm function of your choice on the entire dataset. Your options are: log (Napierian logarithms), log2 (base 2 logarithms), or log10 (base 10 logarithms). Then save to the file type of your choice. (I suggest a ‘.mat’ file,)
For example:
DataSet = randi(10, 5, 3)
LogDataSet = log10(DataSet)
13 个评论
Star Strider
2014-7-2
I have no idea what you are doing. I can’t find any documentation on the ‘dataset’ data type, so you must have created it somehow. If your dataset exists in your workspace as a double array, you should have no problem taking log10 of it.
Panty
2014-7-2
Star Strider
2014-7-2
Negative values create complex logarithms, but it's best to simply take the logs of the positive values.
There is a datasetfun function I haven’t used (it operates similarly to cellfun), but I doubt it would work easily in your situation.
Something similar to this would probably work in your situation:
Data = randi(10, 5, 3)-2
DataPos = find(Data > 0)
LData = log10(Data(DataPos))
LogData = Data;
LogData(DataPos) = LData
The code works. The problem is taking the antilog of it if you want to do that, because negative or zero values are valid logarithms.
Entries such as 2039e+12 aren’t problems, since log10(2039e+12) = 15.3094e+000. This is well within MATLAB’s floating-point ability.
Panty
2014-7-2
Star Strider
2014-7-2
My pleasure!
You can certainly use datasetfun to take the log10 of your data, but selecting for only positive values might require nested datasetfun calls, likely less efficient than converting your data to double and doing the sort of thing I did in my code. You might want to use the table functions instead, since the documentation for the dataset data type says:
- The dataset data type might be removed in a future release. To work with heterogeneous data, use the MATLAB® table data type instead. See MATLAB table documentation for more information.
Panty
2014-7-3
Star Strider
2014-7-3
This seems to work:
D = load('Real GDP_dataset_workspace.mat')
DSC = struct2cell(D);
DS = DSC{1};
Data = double(DS);
DataPos = find(Data > 0);
LData = log10(Data(DataPos));
LogData = Data;
LogData(DataPos) = LData; % Desired Result (Output)
It’s too large for me to look through the entire array, but it works as intended for the smaller test data, so I assume it is working on your full array as well.
Note that the DS variable uses curly braces ‘{}’ to address the contents of the cell as the dataset array.
Star Strider
2014-7-4
My pleasure!
It doesn’t seem to be possible to use datasetfun to do what you want, and to keep the data as a dataset. You need to take it out of the dataset just as I did. If you want to keep it as a dataset, either do as I did, and then create the result as a dataset, or do it in Excel. (I don’t have enough experience with Excel to help you with that.)
Note that your Logdata = log10(data) will not do what you specified. It will take the logs of the negative data as well, leaving you with complex numbers for them, and with -Inf for any that are zero.
Panty
2014-7-4
Star Strider
2014-7-4
I did everything I could to keep them as a dataset and couldn’t. The problem is that taking only the positive values creates vectors of unequal sizes in the dataset, and that is apparently not an option with them. I used the UniformOutput and DatasetOutput options, but without success. I also used my own inline function to select only positive values for the log, but for some reason (I believe it deleted the non-positive values), that failed. The datasetfun function only operates on dataset variables, not specific elements of the variables.
If you have R2013b or later, creating your data as a table using the table functions might allow you to do what you want and keep the string labels. I didn’t try that because you want to keep them as a dataset.
Panty
2014-7-5
Star Strider
2014-7-5
My pleasure!
The dataset class may be very useful in some situations, but it has serious limitations with respect to doing the sort of operation you want to do. The table class is also a core MATLAB set, and so likely portable amongst a number of different applications. I didn’t try table with your data, but I’ll give it a go if you have problems with it in your application.
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