Apply function on specific rows
7 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Hi Everyone,
I am kind of new to MATLAB and have a problem. I used to use, S-Plus and they have a function called "tapply" and I think I am looking for something similar.
Here is the situation, I have time-series database, with a column representing month/year. I would like to apply "mean" function to those rows which have same month/year. For example, if there are 20 unique month/year values, i will have 20 different "mean" each representing, an average of that particular month/year.
Looking forward to responses. Thank you in advance.
1 commentaire
Réponses (2)
Walter Roberson
le 29 Juil 2011
You could use a "for" loop in the general case.
If you are computing a value for each row, you could use
TheValues = arrayfun(@(K) YourFun(YourVariable(K,:)), [list of rows])
For simple functions such as mean, and simple arrays, you can use
TheValues = mean(YourVariable([list of rows],:),2);
The ,2 part tells it to take the mean along the second dimension (rows)
0 commentaires
KKR
le 29 Juil 2011
1 commentaire
Walter Roberson
le 30 Juil 2011
The K is the arglist in the anonymous function; see http://www.mathworks.com/help/techdoc/matlab_prog/f4-70115.html
A list of rows would be like [1 2 3 4 5] or [6 7 8 9] or 1:5 or 6:9 to apply to the designated rows. Your original question did not indicate that your data would always be consecutive so I was thinking that you might have to specify (e.g.) [1 2 6 8 10 11 15]
I do not know how to retrieve a particular row from a database. If the above data were presented in the form of a 9 x 2 cell array, then I would use code such as
mean(vertcat(data{1:6,2}))
To go beyond this, see unique() and ismember(), and look in the MATLAB File Exchange to see if John d'Errico's "consolidator" program is available.
Voir également
Catégories
En savoir plus sur Creating and Concatenating Matrices dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!