Select value from the list by defining criteria

Dear All,

I have a big dataset with the format,

1 2019-09-25 19:33:00 27.7100 86.3200 10 291.122 4.00 1.79 R023E

1 2019-09-25 19:33:00 27.7100 86.3200 10 197.274 4.00 4.44 S8618

1 2019-09-25 19:33:00 27.7100 86.3200 10 170.200 4.00 4.14 RA5AB

I would like to have new set of data

(i) If column 10 has always valule R023E

(ii) If column 7 > 30.00

what is the solution?

Answer 1

[Bob Thompson]

I would use readtable to import the data, the logic indexing to narrow down the results.

data = readtable('mydata.xlsx');
reducedata = data(data(:,10) == 'R023E' & data(:,7) > 30,:);

[Shiba Subedi]

Hello Bob Nbob,

1 '2019-09-25' '19:33:00' 27.71 86.32 197.27 4 4.44 'S8618' 'Dolakha'

Thanks but there is error

Undefined operator '>' for input arguments of type 'table'.

reducedata = data(data(:,9) == 'R023E' & data(:,6) >30,:);

[Bob Thompson]

Mmm, replace 'data(:,6)' with 'data{:,6}'.

Alternatively you can also use 'data.*variable name*' if you know what the consistent variable name is.

[Bob Thompson]

I tried a sample using your conditions:

data = randi(100,20,1);
data = array2table(data); % Create a table of random numbers up to 100.
reducedata = data(data{:,1}>10^1.5 & data{:,1}<10^1.9,:);

This produces a result, which makes me think that maybe there's something wrong with the logic you're trying to check. Are you sure that your data set contains the values you're looking for? I wouldn't be able to check it without having a sample of your dataset.

[Adam Danz]

Shiba Subedi's answer moved here as a comment. Please use the comment section for discussion and the answer section to propose answers.

[Adam Danz]

Use dot indexing when working with columns from a table, not subscript indexing in curly brackets.

Could you share the result of the line below?

head(data)  % data is the output from readtable

[Bob Thompson]

I would agree that dot indexing is more efficient, but I assumed that variable names were inconsistent or unknown.

[Adam Danz]

That's a good point. However, the variable names can be set in readtable() or after the table is created. If it is known that the data in column #7 is needed, they can name that column anything they want.