I'm using randomForest in order to find out the most significant variables. I was expecting some output that defines the accuracy of the model and also ranks the variables based on their importance. But I am a bit confused now. I tried randomForest and then ran importance() to extract the importance of variables.
But then I saw another command rfcv (Random Forest Cross-Valdidation for feature selection), which should be the most appropriate for this purpose I suppose, but the question I have regarding this is: how to get the list of the most important variables? How to see the output after running it? Which command to use?
Another thing: What is the difference between randomForest and predict.randomForest?
I am not very familiar with randomforest and R therefore any help would be appreciated.
Thank you in advance!
After you have made a randomForest model you use predict.randomForest to use the model you created on new data e.g. build a random forest with training data then run your validation data through that model with predict.randomForest.
As for the rfcv there is an option recursive which (from the help):
whether variable importance is (re-)assessed at each step of variable
reduction
Its all in the help file
Related
I am using glmulti to select a set of candidate generalized linear models and my variable importance values and 'best' model keep changing each time I run the model.
I am struggling to understand why this is, does glmulti need a set.seed value to make results reproducible?
Thanks.
I believe the glmulti function is in the glmulti package. (You should state this in your question...) If so, the help page says that sometimes it uses a genetic algorithm to find the best model. Those are indeed random algorithms, so you can expect to get an answer that depends on the random number seed.
I'm using the "party" package to create random forest of regression trees.
I've created a ForestControl class in order to limit my number of trees (ntree), of nodes (maxdepth) and of variables I use to fit a tree (mtry).
One thing I'm not sure of is if the cforest algo is using subsets of my training set for each tree it generates or not.
I've seen in the documentation that it is bagging so I assume it should. But I'm not sure to understand well what the "subset" input is in that function.
I'm also puzzled by the results I get using ctree: when plotting the tree, I see that all my variables of my training set are classified in the different terminal tree nodes while I would have exepected that it only uses a subset here too.
So my question is, is cforest doing the same thing as ctree or is it really bagging my training set?
Thanks in advance for you help!
Ben
This is a follow-up to a previous question I asked a while back that was recently answered.
I have built several gbm models with dismo::gbm.step, which relies on the gbm fitting functions found in R package gbm, as well as cross validation tools from R package splines.
As part of my analysis, I would like to use some of the graphical tools available in R (e. g. perspective plots) to visualize pairwise interactions in the data. Both the gbm and the dismo packages have functions for detecting and modelling interactions in the data.
The implementation in dismo is explained in Elith et. al (2008) and returns a statistic which indicates departures of the model predictions from a linear combination of the predictors, while holding all other predictors at their means.
The implementation in gbm uses Friedman`s H statistic (Friedman & Popescue, 2005), and returns a different metric, and also does NOT set the other variables at their means.
The interactions modelled and plotted with dismo::gbm.interactions are great and have been very informative. However, I would also like to use gbm::interact.gbm, partly for publication strength and also to compare the results from the two methods.
If I try to run gbm::interact.gbm in a gbm.object created with dismo, an error is returned…
"Error in is.factor(data[, x$var.names[j]]) :
argument "data" is missing, with no default"
I understand dismo::gmb.step adds extra data the authors thought would be useful to the gbm model.
I also understand that the answer to my question lies somewherein the source code.
My questions is...
Is it possible to modify a gbm object created in dismo to be used in gbm::gbm.interact? If so, would this be accomplished by...
a. Modifying the gbm object created in dismo::gbm.step?
b. Modifying the source code for gbm::interact.gbm?
c. Doing something else?
I will be going through the source code trying to solve this myself, if I come up with a solution before anyone answers I will answer my own question.
The gbm::interact.gbm function requires data as an argument interact.gbm <- function(x, data, i.var = 1, n.trees = x$n.trees).
The dismo gbm.object is essentially the same as the gbm gbm.object, but with extra information attached so I don't imagine changing the gbm.object would help.
I hope I have come to the right forum. I'm an ecologist making species distribution models using the maxent (version 3.3.3, http://www.cs.princeton.edu/~schapire/maxent/) function in R, through the dismo package. I have used the argument "replicates = 5" which tells maxent to do a 5-fold cross-validation. When running maxent from the maxent.jar file directly (the maxent software), an html file with statistics will be made, including the prediction maps. In R, an html file is also made, but the prediction maps have to be extracted afterwards, using the function "predict" in the dismo package in r. When I do this, I get 5 maps, due to the 5-fold cross-validation setting. However, (and this is the problem) I want only one output map, one "summary" prediction map. I assume this is possible, although I don't know how maxent computes it. The maxent tutorial (see link above) says that:
"...you may want to avoid eating up disk space by turning off the “write output grids” option, which will suppress writing of output grids for the replicate runs, so that you only get the summary statistics grids (avg, stderr etc.)."
A list of arguments that can be put into R is found in this forum https://groups.google.com/forum/#!topic/maxent/yRBlvZ1_9rQ.
I have tried to use the argument "outputgrids=FALSE" both in the maxent function itself, and in the predict function, but it doesn't work. I still get 5 maps, even though I don't get any errors in R.
So my question is: How do I get one "summary" prediction map instead of the five prediction maps that results from the cross-validation?
I hope someone can help me with this, I am really stuck and haven't found any answers anywhere on the internet. Not even a discussion about this. Hope my question is clear. This is the R-script that I use:
model1<-maxent(x=predvars, p=presence_points, a=target_group_absence, path="//home//...//model1", args=c("replicates=5", "outputgrids=FALSE"))
model1map<-predict(model1, predvars, filename="//home//...//model1map.tif", outputgrids=FALSE)
Best regards,
Kristin
Sorry to be the bearer of bad news, but based on the source code, it looks like Dismo's predict function does not have the ability to generate a summary map.
Nitty-gritty details for those who care: When you call maxent with replicates set to something greater than 1, the maxent function returns a MaxEntReplicates object, rather than a normal MaxEnt object. When predict receives a MaxEntReplicates object, it just iterates through all of the models that it contains and calls predict on them individually.
So, what next? Fortunately, all is not lost! The reason that Dismo doesn't have this functionality is that for most kinds of model-building, there isn't actually a valid way to average parameters across your cross-validation models. I don't want to go so far as to say that that's definitely the case for MaxEnt specifically, but I suspect it is. As such, cross-validation is usually used more as a way of checking that your model building methodology works for your data than as a way of building your model directly (see this question for further discussion of that point). After verifying via cross-validation that models built using a given procedure seem to be accurate for the phenomenon you're modelling, it's customary to build a final model using all of your data. In theory this new model should only be better than models trained on a subset of your data.
So basically, assuming your cross-validated models look reasonable, you can run MaxEnt again with only one replicate. Your final result will be a model accuracy estimate based on the cross-validation and a map based on the second run with all of your data lumped together. Depending on what exactly your question is, there might be other useful summary statistics from the cross-validation that you want to use, but those are all things you've already seen in the html output.
I may have found this a couple of years later. But you could do something like this:
xm <- maxent(predictors, pres_train) # basically the maxent model
px <- predict(predictors, xm, ext=ext, progress= '' ) #prediction
px2 <- predict(predictors, xm2, ext=ext, progress= '' ) #prediction #02
models <- stack(px,px2) # create a stack of prediction from all the models
final_map <- mean(px,px2) # Take a mean of all the prediction
plot(final_map) #plot the averaged map
xm1,xm2,.. would be the maxent models for each partitions in cross-validation, and px, px2,.. would be the predicted maps.
Is it possible to do regressions in R using a panel data set with a binary dependent variable? I am familiar with using glm for logit and probit and plm for panel data, but am not sure how to combine the two. Are there any existing code examples?
EDIT
It would also be helpful if I could figure out how to extract the matrix that plm() is using when it does a regression. For instance, you could use plm to do fixed effects, or you could create a matrix with the appropriate dummy variables and then run that through glm(). In a case like this, however, it is annoying to generate the dummies yourself and it would be easier to have plm do it for you.
The package "pglm" might be what you need.
http://cran.r-project.org/web/packages/pglm/pglm.pdf
This package offers some functions of glm-like models for panel data.
Maybe the package lme4 is what you are looking for.
It seems to be possible to run generalized regressions with fixed effects using the comand glme.
But you should be aware that panel data with binary dependent variable is different than the usual linear models.
This site may be helpful.
Best regards,
Manoel
model.frame(plmmodel)
will give you the data frame that is actually used by plm for fitting the model (i.e. after list-wise deletion if you have NAs, etc.)
I don't think that plm has implemented functions to estimate models with binary outcomes, but I may be wrong. Check out the reference manual at: http://cran.r-project.org/web/packages/plm/index.html
If I'm right, this would suggest that you can't "combine the two" without considerable work in extending the functions provided by plm.