使用 apply 系列函数替换 R 中的嵌套 for 循环 [英] Using apply family of functions to replace nested for loop in R

问题描述

我写了一个接受 3 个参数的函数:

I wrote a function that takes 3 arguments:

download_data <- function(team, year, df) {
    ...
}

我想用两个字符向量分别为上述函数提供第一个和第二个参数，以便向量的每个组合被调用一次:

I have two character vectors that I want to use to provide the first and second argument respectively to the above function, so that each combination of the vectors is called once:

nfl_teams <- c("bills", "dolphins", "jets", "patriots")

years <- c("2002", "2003", "2004", "2005")

我可以使用嵌套的 for 循环很容易地做到这一点:

I can do so fairly easily using a nested for loop:

for (i in 1:4) {
  for ( j in 1:4) {
    salary_data <- download_data(nfl_teams[i], years[j], salary_data)
  }
}

然而，这似乎是一个un-R"方法来实现这一点，最好使用 apply 函数之一.然而，在阅读并尝试了所有这些之后，我无法完成这个看似简单的任务.

However, it seems that this an "un-R" way to accomplish this, and it would be better to use one of the apply functions. However, after reading through all of them and trying them out, I was unable to accomplish this seemingly simple task.

看起来这可能是一个矩阵，因此 apply 会起作用吗?

It seems like maybe this would be a matrix, thus apply would work?

推荐答案

你可以像循环一样使用 apply 函数，除了语法不同

You can use the apply functions just like loops, except with different syntax

dummy <- function(x, y) paste(x, y)
sapply(1:4, function(i) sapply(1:4, function(j) dummy(nfl_teams[i], years[j])))

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