Thank you Paul for all information you have provided me.

Actually, in my work I check many parameter of random forest but one that I couldn't calculate yet (and need it certainly) is the number of nodes in each tree of random forest. I use 'randomForest' package in R in order to generate my model. But I couldn't find any function presents me the random forest structure(form each DT structure point of view).

That is really helpful, thank you so much

Hi,

If you wish to visualize what the Random Forest has learned, you can use a simple technique that is described in this paper http://dx.doi.org/10.1016/j.ins.2012.10.039 and available in the rminer package (version 1.2):

http://cran.r-project.org/web/packages/rminer/index.html

Regards,

Paulo Cortez

Also to visualize what the Random Forest has learned, try the R CRAN package forestFloor. See forestFloor.dk for latest news and publications.

http://forestFloor.dk

To explore individual trees in your forest, you can use the getTree() function. I also find it helpful to explore the information available in str(your_random_forest_model), particularly your_random_forest_model$forest. 

by using getTree function 

I also found the getTree function useful.

visreg: Visualization of Regression Models

Provides a convenient interface for constructing plots to visualize the fit of regression models arising from a wide variety of models in R ('lm', 'glm', 'coxph', 'rlm', 'gam', 'locfit', 'randomForest', etc.)