128 lines
4.8 KiB
R
128 lines
4.8 KiB
R
# load xgboost library
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require(xgboost)
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require(methods)
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# helper function to read libsvm format
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# this is very badly written, load in dense, and convert to sparse
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# use this only for demo purpose
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# adopted from https://github.com/zygmuntz/r-libsvm-format-read-write/blob/master/f_read.libsvm.r
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read.libsvm <- function(fname, maxcol) {
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content <- readLines(fname)
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nline <- length(content)
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label <- numeric(nline)
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mat <- matrix(0, nline, maxcol+1)
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for (i in 1:nline) {
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arr <- as.vector(strsplit(content[i], " ")[[1]])
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label[i] <- as.numeric(arr[[1]])
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for (j in 2:length(arr)) {
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kv <- strsplit(arr[j], ":")[[1]]
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# to avoid 0 index
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findex <- as.integer(kv[1]) + 1
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fvalue <- as.numeric(kv[2])
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mat[i,findex] <- fvalue
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}
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}
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mat <- as(mat, "sparseMatrix")
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return(list(label=label, data=mat))
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}
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# test code here
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dtrain <- xgb.DMatrix("agaricus.txt.train")
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dtest <- xgb.DMatrix("agaricus.txt.test")
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param = list("bst:max_depth"=2, "bst:eta"=1, "silent"=1, "objective"="binary:logistic")
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watchlist <- list("eval"=dtest,"train"=dtrain)
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# training xgboost model
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bst <- xgb.train(param, dtrain, nround=2, watchlist=watchlist)
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# make prediction
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preds <- xgb.predict(bst, dtest)
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labels <- xgb.getinfo(dtest, "label")
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err <- as.numeric(sum(as.integer(preds > 0.5) != labels)) / length(labels)
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# print error rate
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print(paste("error=",err))
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# dump model
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xgb.dump(bst, "dump.raw.txt")
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# dump model with feature map
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xgb.dump(bst, "dump.nice.txt", "featmap.txt")
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# save dmatrix into binary buffer
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succ <- xgb.save(dtest, "dtest.buffer")
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# save model into file
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succ <- xgb.save(bst, "xgb.model")
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# load model and data in
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bst2 <- xgb.Booster(modelfile="xgb.model")
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dtest2 <- xgb.DMatrix("dtest.buffer")
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preds2 <- xgb.predict(bst2, dtest2)
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# assert they are the same
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stopifnot(sum(abs(preds2-preds)) == 0)
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###
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# build dmatrix from sparseMatrix
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###
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print ('start running example of build DMatrix from R.sparseMatrix')
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csc <- read.libsvm("agaricus.txt.train", 126)
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label <- csc$label
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data <- csc$data
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dtrain <- xgb.DMatrix(data, info=list(label=label) )
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watchlist <- list("eval"=dtest,"train"=dtrain)
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bst <- xgb.train(param, dtrain, nround=2, watchlist=watchlist)
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###
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# build dmatrix from dense matrix
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###
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print ('start running example of build DMatrix from R.Matrix')
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mat = as.matrix(data)
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dtrain <- xgb.DMatrix(mat, info=list(label=label) )
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watchlist <- list("eval"=dtest,"train"=dtrain)
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bst <- xgb.train(param, dtrain, nround=2, watchlist=watchlist)
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###
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# advanced: cutomsized loss function
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#
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print("start running example to used cutomized objective function")
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# note: for customized objective function, we leave objective as default
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# note: what we are getting is margin value in prediction
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# you must know what you are doing
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param <- list("bst:max_depth" = 2, "bst:eta" = 1, "silent" =1)
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# user define objective function, given prediction, return gradient and second order gradient
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# this is loglikelihood loss
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logregobj <- function(preds, dtrain) {
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labels <- xgb.getinfo(dtrain, "label")
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preds <- 1.0 / (1.0 + exp(-preds))
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grad <- preds - labels
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hess <- preds * (1.0-preds)
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return(list(grad=grad, hess=hess))
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}
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# user defined evaluation function, return a list(metric="metric-name", value="metric-value")
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# NOTE: when you do customized loss function, the default prediction value is margin
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# this may make buildin evalution metric not function properly
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# for example, we are doing logistic loss, the prediction is score before logistic transformation
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# the buildin evaluation error assumes input is after logistic transformation
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# Take this in mind when you use the customization, and maybe you need write customized evaluation function
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evalerror <- function(preds, dtrain) {
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labels <- xgb.getinfo(dtrain, "label")
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err <- as.numeric(sum(labels != (preds > 0.0))) / length(labels)
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return(list(metric="error", value=err))
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}
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# training with customized objective, we can also do step by step training
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# simply look at xgboost.py"s implementation of train
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bst <- xgb.train(param, dtrain, nround=2, watchlist, logregobj, evalerror)
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###
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# advanced: start from a initial base prediction
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#
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print ("start running example to start from a initial prediction")
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# specify parameters via map, definition are same as c++ version
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param = list("bst:max_depth"=2, "bst:eta"=1, "silent"=1, "objective"="binary:logistic")
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# train xgboost for 1 round
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bst <- xgb.train( param, dtrain, 1, watchlist )
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# Note: we need the margin value instead of transformed prediction in set_base_margin
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# do predict with output_margin=True, will always give you margin values before logistic transformation
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ptrain <- xgb.predict(bst, dtrain, outputmargin=TRUE)
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ptest <- xgb.predict(bst, dtest, outputmargin=TRUE)
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succ <- xgb.setinfo(dtrain, "base_margin", ptrain)
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succ <- xgb.setinfo(dtest, "base_margin", ptest)
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print ("this is result of running from initial prediction")
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bst <- xgb.train( param, dtrain, 1, watchlist )
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