Nothing

```
loss.function = function(fitted, data, loss, extra.args, debug = FALSE) {
if (loss %in% c("logl", "logl-g", "logl-cg")) {
result = entropy.loss(fitted = fitted, data = data, debug = debug)
}#THEN
else if (loss %in% c("pred", "pred-exact", "pred-lw", "pred-lw-cg")) {
result = classification.error(node = extra.args$target, fitted = fitted,
prior = extra.args$prior, n = extra.args$n,
from = extra.args$from, data = data, loss = loss, debug = debug)
}#THEN
else if (loss %in% c("cor", "cor-lw", "cor-lw-cg")) {
result = predictive.correlation(node = extra.args$target, fitted = fitted,
n = extra.args$n, from = extra.args$from, data = data,
loss = loss, debug = debug)
}#THEN
else if (loss %in% c("mse", "mse-lw", "mse-lw-cg")) {
result = mean.square.error(node = extra.args$target, fitted = fitted,
n = extra.args$n, from = extra.args$from, data = data,
loss = loss, debug = debug)
}#THEN
if (debug)
cat(" @ total loss is", result$loss, ".\n")
return(result)
}#LOSS.FUNCTION
# how to aggregate loss functions across the folds of cross-validation.
kfold.loss.postprocess = function(kcv, kcv.length, loss, extra.args, data) {
if (loss %in% c("cor", "cor-lw")) {
if (all(is.na(unlist(sapply(kcv, "[", "loss"))))) {
# this happens for root nodes, whose predictions are just the mean of
# the response over the test set; propagate the NAs to the CV estimate.
mean = NA
}#THEN
else {
# match predicted and observed values.
pred = unlist(lapply(kcv, "[[", "predicted"))
obs = unlist(lapply(kcv, "[[", "observed"))
# compute the predictive correlation.
mean = cor(obs, pred)
}#ELSE
}#THEN
else {
# compute the mean of the observed values of the loss function, weighted
# to account for unequal-length splits.
mean = weighted.mean(unlist(sapply(kcv, '[', 'loss')), kcv.length)
}#ELSE
return(mean)
}#LOSS.POSTPROCESS
# predictive mean square error for gaussian networks.
mean.square.error = function(node, fitted, n, from, data, loss, debug = FALSE) {
if (loss == "mse")
pred = gaussian.prediction(node, fitted, data)
else if (loss %in% c("mse-lw", "mse-lw-cg"))
pred = map.prediction(node, fitted, data, n = n, from = from)
return(list(loss = mean((data[, node] - pred)^2), predicted = pred,
observed = data[, node]))
}#MEAN.SQUARE.ERROR
# predictive correlation for gaussian networks.
predictive.correlation = function(node, fitted, n, from, data, loss,
debug = FALSE) {
if (loss == "cor")
pred = gaussian.prediction(node, fitted, data)
else if (loss %in% c("cor-lw", "cor-lw-cg"))
pred = map.prediction(node, fitted, data, n = n, from = from)
if (((loss == "cor") && length(fitted[[node]]$parents) == 0))
return(list(loss = NA, predictions = pred, observed = data[, node]))
else
return(list(loss = cor(data[, node], pred), predicted = pred,
observed = data[, node]))
}#PREDICTIVE.CORRELATION
# log-likelihood loss function for gaussian and discrete networks.
entropy.loss = function(fitted, data, keep = names(fitted), by.sample = FALSE,
debug = FALSE) {
list(loss = .Call(call_entropy_loss,
fitted = fitted,
data = data,
by.sample = by.sample,
keep = keep,
debug = debug))
}#ENTROPY.LOSS
# classification error as a loss function.
classification.error = function(node, fitted, prior = NULL, n, from, data,
loss, debug = FALSE) {
if (loss == "pred-exact")
pred = naive.classifier(node, fitted, prior, data)
else if (loss == "pred")
pred = discrete.prediction(node, fitted, data)
else if (loss %in% c("pred-lw", "pred-lw-cg"))
pred = map.prediction(node, fitted, data, n = n, from = from)
l = .Call(call_class_err,
reference = .data.frame.column(data, node),
predicted = pred)
if (debug)
cat(" > classification error for node", node, "is", l, ".\n")
return(list(loss = l, predicted = pred, observed = data[, node]))
}#CLASSIFICATION.ERROR
```

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