使用多列作为变量与 sapply [英] use multiple columns as variables with sapply

问题描述

我有一个 dataframe，我想应用一个函数来获取三列的值并计算三个值之间的最小差异.

I have a dataframe and I would like to apply a function that takes the values of three columns and computes the minimum difference between the three values.

#dataset
df <- data.frame(a= sample(1:100, 10),b = sample(1:100, 10),c= sample(1:100, 10))

#function
minimum_distance <- function(a,b,c)
{
  dist1 <- abs(a-b)
  dist2 <- abs(a-c)
  dist3 <- abs(b-c)
  return(min(dist1,dist2,dist3))
}

我正在寻找类似的东西:

I am looking for something like:

df$distance <- sapply(df, function(x) minimum_distance(x$a,x$b,x$c) )
## errormessage
Error in x$a : $ operator is invalid for atomic vectors

虽然我可以使用 ddply:

While I can use ddply:

df2 <- ddply(df,.(a),function(r) {data.frame(min_distance=minimum_distance(r$a,r$b, r$c))}, .drop=FALSE)

这不会保留所有列.有什么建议吗?

This doesn't keep all of the columns. Any suggestions?

我最终使用了:

df$distance <- mapply(minimum_distance, df$a, df$b, df$c)

推荐答案

尝试 mapply():

Try mapply():

qq <- mapply(minimum_distance, df$a, df$b, df$c)

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