MATLAB Array comparisons

Question

I am just learning MATLAB for the first time.

I am reading some code trying to understand it. I believe I have two arrays below called pdw_raw & pdw_factors which contains a list of dates. The line that is causing me most confusion is the last line in the code below. The only way I can seem to make sense of this line is that every element in pdw_raw is being check against the max date of pdw_factors - is this correct?

Find the MATLAB syntax hard to understand at the moment.

%first retrieve the relevant dates;
sql_statement   = ['select distinct pricedatew from D_RAWRETS order by pricedatew'];
cursor          = exec(QES_DB, sql_statement);
cursor          = fetch(cursor);
pdw_raw         = datenum(cursor.data);
pdw_raw         = pdw_raw(1:end-1, 1);

sql_statement   = ['select distinct pricedatew from D_FACTORS order by pricedatew'];
cursor          = exec(QES_DB, sql_statement);
cursor          = fetch(cursor);
pdw_factors     = datenum(cursor.data);

missing_dates   = pdw_raw(pdw_raw > max(pdw_factors));

Dan · Accepted Answer · 2014-02-19 09:39:37Z

2

That is correct.

pdw_raw > max(pdw_factors) creates an array of logicals that is true for elements of pdw_raw that are bigger than the largest pdw_factors elements, and false otherwise.

pdw_raw(pdw_raw > max(pdw_factors)); uses logical indexing to extract only the elements for which pdw_raw > max(pdw_factors) is true.

answered Feb 19, 2014 at 9:39

Dan

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3 Comments

Stewie Griffin Over a year ago

+1, @mHelpMe: Note that max returns a vector if the input argument is a 2D-matrix. I.e. it returns the maximum value of each column, not the overall maximum as a single number.

Dan Over a year ago

@RobertP. true, but in this case pwd_factors comes from a sql query that only selects a single column so it is safe to assume that it is a vector.

Stewie Griffin Over a year ago

I know =) It was just a small reminder to OP, as it is not intuitive and could easily cause problems in other situations.

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