Question

我希望有一个等效的Excel函数“if”。这似乎很基本，但我找不到相关的帮助。

如果不同列中的两个后续单元格不相同，我想评估特定单元格的“NA”。在Excel中，命令将如下（例如在C1中）：if（A1 = A2，B1，“NA”）。然后我只需将其扩展到列的其余部分。

但在R中，我被困住了！

到目前为止，这是我的R代码的等价物。

df = data.frame(Type = c("1","2","3","4","4","5"),
                File = c("A","A","B","B","B","C"))
df

为了在另一列中获得每个Type的以下类型，我在StackOverflow上找到了一个有用的函数来完成这项工作。

# determines the following Type of each Type
shift <- function(x, n){
  c(x[-(seq(n))], rep(6, n))
}

df$TypeFoll <- shift(df$Type, 1)
df

现在，当这行的文件与下一行的文件相同时，我想将TypeFoll保留在特定的行中。

这是我尝试过的。它失败了！

for(i in 1:length(df$File)){
df$TypeFoll2 <- ifelse(df$File[i] == df$File[i+1], df$TypeFoll, "NA")
}

df

最后，我的数据框应如下所示：

aim = data.frame(Type = c("1","2","3","4","4","5"),
                 File = c("A","A","B","B","B","C"),
                 TypeFoll = c("2","3","4","4","5","6"),
                 TypeFoll2 = c("2","NA","4","4","NA","6"))
aim

哦，顺便说一句，如果有人知道如何轻松地将TypeFoll和TypeFoll2列放在Type Type之后，那就太棒了！

提前致谢

Answer 1

我会这样做（不保留移位函数的结果）

df = data.frame(Type = c("1","2","3","4","4","5"),
                File = c("A","A","B","B","B","C"), stringsAsFactors = FALSE)

# This is your shift function
len=nrow(df)
A1 <- df$File[1:(len-1)]
A2 <- df$File[2:len]
# Why do you save the result of the shift function in the df?

然后分配if(A1 = A2, B1, "NA")。正如akrun提到的ifelse是矢量化的：顺便说一句。这是将列附加到data.frame

的方法

df$TypeFoll2 <- c(ifelse(A1 == A2, df$Type, NA), 6) #Why 6?

因为6这里的硬编码类似于：

df$TypeFoll2 <- c(ifelse(A1 == A2, df$Type, NA), max(df$Type)+1)

更通用。

Answer 2

首先，＆＃39;对于＆＃39; R中的循环非常慢，所以请尝试将其视为向量操作。

df = data.frame(Type = c("1","2","3","4","4","5"),
                File = c("A","A","B","B","B","C"));

创建已移位的类型和文件并将其放在新列中：

df$TypeFoll = c(as.character(df$Type[2:nrow(df)]), "NA");
df$FileFoll = c(as.character(df$File[2:nrow(df)]), "NA");

现在，df看起来像这样：

> df
  Type File TypeFoll FileFoll
1    1    A        2        A
2    2    A        3        B
3    3    B        4        B
4    4    B        4        B
5    4    B        5        C
6    5    C       NA       NA

然后，通过组合这些来创建TypeFoll2：

df$TypeFoll2 = ifelse(df$File == df$FileFoll, df$TypeFoll, "NA");

你应该有一些看起来很像你想要的东西：

> df;
  Type File TypeFoll FileFoll TypeFoll2
1    1    A        2        A         2
2    2    A        3        B        NA
3    3    B        4        B         4
4    4    B        4        B         4
5    4    B        5        C        NA
6    5    C       NA       NA        NA

如果要删除FileFoll列： df $ FileFoll = NULL;

如何根据另一列中的条件更改数据框列中的值？

2 个答案: