使用ifelse将值分配给R中的新数据框列 [英] Use of ifelse to assign values to a new dataframe column in R

问题描述

我有一个时间序列数据帧，想创建一个新的数字列，其值是现有数字列的函数，并根据星期几列进行分配.

I have a time series dataframe and would like to create a new numeric column with values which are a function of an existing numeric column and which are assigned according to the day of the week column.

例如，我将需要以下代码:

For example, I would require something like the following code:

Day <- c("Mo", "Mo", "Mo", "Tu", "Tu", "We", "We", "We", "We", "Th")
Val <- c(1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000)
df <- data.frame(cbind(Day,Val))
df$Adj <- ifelse(df$Day == "Mo" || df$Day == "Tu", 
                 as.numeric(levels(df$Val)) + 1, 
                 as.numeric(levels(df$Val)) + 2)

返回:

   Day  Val  Adj
1   Mo 1000 1001
2   Mo 1000 1001
3   Mo 1000 1001
4   Tu 1000 1001
5   Tu 1000 1001
6   We 1000 1002
7   We 1000 1002
8   We 1000 1002
9   We 1000 1002
10  Th 1000 1002

不幸的是，我的代码只返回Adj作为1001s列.

Unfortunately for me, my code instead returns Adj as a column of 1001s only.

   Day  Val  Adj
1   Mo 1000 1001
2   Mo 1000 1001
3   Mo 1000 1001
4   Tu 1000 1001
5   Tu 1000 1001
6   We 1000 1001
7   We 1000 1001
8   We 1000 1001
9   We 1000 1001
10  Th 1000 1001

我已经在"We"其中之一上测试了ifelse行，就可以了...

I've tested the ifelse on one of the "We" rows and it does the trick ...

> ifelse(df$Day[6] == "Mo" || df$Day[6] == "Tu", 
+        as.numeric(levels(df$Val[6])) + 1, 
+        as.numeric(levels(df$Val[6])) + 2)
[1] 1002

...但是我似乎无法使它在整个列上都能正常工作，据我了解，这是ifelse函数相对于循环的if-else语句的优势之一.

... but I can't seem to get it to work on an entire column, which I had understood is one of the advantages of the ifelse function over a looped if-else statement.

我的方法基于我能找到的最相似的问题(使用if {} else {}中的)，但没有任何喜悦.我在这里想念什么?

I'm basing my approach off of the most similar questions I could find (Create new column in dataframe using if {} else {} in R) but have had no joy. What am I missing here?

推荐答案

我们可以使用％in％来检查 Day 是否具有作为 c('Mo'，'Tu')，相应地在 Val 中添加1或2.

We can use %in% to check if Day has value as c('Mo', 'Tu'), add 1 or 2 accordingly to Val.

df <- transform(df, Adj = Val + ifelse(Day %in% c('Mo', 'Tu'), 1, 2))
#you can do this without `ifelse` as well.
#df <- transform(df, Adj = Val + as.integer(!Day %in% c('Mo', 'Tu')) + 1)
df

#   Day  Val  Adj
#1   Mo 1000 1001
#2   Mo 1000 1001
#3   Mo 1000 1001
#4   Tu 1000 1001
#5   Tu 1000 1001
#6   We 1000 1002
#7   We 1000 1002
#8   We 1000 1002
#9   We 1000 1002
#10  Th 1000 1002

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