此功能中-c和nrow的目的是什么？
bdf <- by(bdf, bdf$Serial_number, function(SN, k) {
SN[-c(1:k, (nrow(SN)-k+1):nrow(SN)),]
}, k = 10)
by()将数据帧bdf除以第二个参数Serial_number，apply将函数函数（SN，k）拆分为第三个参数。我不明白这个功能的主体。
答案 0 :(得分：5)
LinkedList创建一个向量。 struct node {
struct node *next;
int score;
};
/* Assumes that head is not NULL */
void remove_lowest(struct node **head)
{
if (*head) {
struct node *current = *head;
struct node *prev = NULL;
struct node *lowest = current;
struct node *low_prev = NULL;
int low_score = current->score;
while (current) {
if (current->score < low_score) {
lowest = current;
low_prev = prev;
low_score = current->score;
}
prev = current;
current = current->next;
}
if (low_prev == NULL) { // first node is lowest
*head = (*head)->next;
} else if (lowest->next == NULL) { // last node is lowest
low_prev->next = NULL;
} else {
low_prev->next = lowest->next;
}
free(lowest);
}
}
使向量中的数字为负数。向量位于＆＃34;行＆＃34; c()的位置，因此省略了从1到-，从[到数据框末尾的行。因此，它会截断数据框的第一行k和最后nrow(SN) - k + 1行。