在 R 中使用函数和 mapply 创建新列以求和其他列

Question

假设，我有一个数据框 df，我想在添加两个现有列“a”和“b”的基础上创建一个名为“c”的新列。我只会运行以下代码：

df$c <- df$a + df$b

但我也想对许多其他专栏执行此操作。那么为什么我的下面的代码不起作用？

# Reproducible data:

martial_arts <- data.frame(gym_branch=c("downtown_a", "downtown_b", "uptown", "island"),
                           day_boxing=c(5,30,25,10),day_muaythai=c(34,18,20,30),
                           day_bjj=c(0,0,0,0),day_judo=c(10,0,5,0),
                           evening_boxing=c(50,45,32,40), evening_muaythai=c(50,50,45,50),
                           evening_bjj=c(60,60,55,40), evening_judo=c(25,15,30,0))

# Creating a list of the new column names of the columns that need to be added to the martial_arts dataframe:

pattern<-c("_boxing","_muaythai","_bjj","_judo")
d<- expand.grid(paste0("martial_arts$total",pattern))

# Creating lists of the columns that will be added to each other:

e<- names(martial_arts %>% select(day_boxing:day_judo))
f<- names(martial_arts %>% select(evening_boxing:evening_judo))

# Writing a function and using mapply:

kick_him <- function(d,e,f){d <- rowSums(martial_arts[ , c(e, f)], na.rm=T)}

mapply(kick_him,d,e,f)

现在，mapply 根据加法生成正确的结果：

> mapply(ff,d,e,f)
     Var1 <NA> <NA> <NA>
[1,]   55   84   60   35
[2,]   75   68   60   15
[3,]   57   65   55   35
[4,]   50   80   40    0

但它不会将新列添加到 martial_arts 数据框。理论上的功能应该做以下事情

martial_arts$total_boxing <- martial_arts$day_boxing + martial_arts$evening_boxing
...
...
martial_arts$total_judo <- martial_arts$day_judo + martial_arts$evening_judo

并将四个新的总计列添加到 martial_arts。

那我做错了什么？

Answer 1

这里的赋值是错误的，即 martial_arts$total_boxing 不是一个字符串，它应该是单独的“total_boxing”，并且它应该在 Map/mapply 的 lhs 上。由于 OP 已经在 'd' 数据集中创建了 'martial_arts$' 作为列，我们将删除前缀部分并进行赋值

kick_him <- function(e,f){rowSums(martial_arts[ , c(e, f)], na.rm=TRUE)}
martial_arts[sub(".*\$", "", d$Var1)] <- Map(kick_him, e, f)

-现在检查数据集

> martial_arts
  gym_branch day_boxing day_muaythai day_bjj day_judo evening_boxing evening_muaythai evening_bjj evening_judo total_boxing total_muaythai total_bjj total_judo
1 downtown_a          5           34       0       10             50               50          60           25           55             84        60         35
2 downtown_b         30           18       0        0             45               50          60           15           75             68        60         15
3     uptown         25           20       0        5             32               45          55           30           57             65        55         35
4     island         10           30       0        0             40               50          40            0           50             80        40          0

在 R 中使用函数和 mapply 创建新列以求和其他列

Using a function and mapply in R to create new columns that sums other columns

r

function

apply

mapply