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r - 如何解决 R 中的矢量化问题？

问题描述

R新手（ish）。我已经编写了一些在 R 中使用for()循环的代码。我想以矢量化形式重写它，但它不起作用。

用于说明的简化示例：

library(dplyr)

x <- data.frame(name = c("John", "John", "John", "John", "John", "John", "John", "John", "Fred", "Fred"),
                year = c(1, NA, 2, 3, NA, NA, 4, NA, 1, NA))

## if year is blank and name is same as name from previous row
##    take year from previous row
## else
##    stick with the year you already have

# 1. Run as a loop

x$year_2 <- NA
x$year_2[1] <- x$year[1]                

for(row_idx in 2:10)
{
  if(is.na(x$year[row_idx]) & (x$name[row_idx] == x$name[row_idx - 1]))
  {
    x$year_2[row_idx] = x$year_2[row_idx - 1]
  }
  else
  {
    x$year_2[row_idx] = x$year[row_idx]
  }
}  

# 2. Attempt to vectorise

x <- data.frame(name = c("John", "John", "John", "John", "John", "John", "John", "John", "Fred", "Fred"),
                year = c(1, NA, 2, 3, NA, NA, 4, NA, 1, NA))

x$year_2 <- ifelse(is.na(x$year) & x$name == lead(x$name),
                   lead(x$year_2),
                   x$year)

我认为矢量化版本被搞砸了，因为它有一个循环性（即x$year_2出现在 的两侧<-）。有没有办法解决这个问题？

谢谢你。

标签： rvectorization

解决方案

我建议你使用已经建立的功能，R一开始感觉很难，因为我们被训练去重新发明轮子，不要这样做。

library(tidyverse)

x <- data.frame(name = c("John", "John", "John", "John", "John", "John", "John", "John", "Fred", "Fred"),
                year = c(1, NA, 2, 3, NA, NA, 4, NA, 1, NA))


x %>% 
  group_by(name) %>% 
  tidyr::fill(year)

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