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I have a two column dataframe in R and i want to add a third column with values that are a function of the first two. As long as the function is a simple mathematical formula no problem data$c <- data$a*15 - 10 + data$b*0.5 But my function is non continous and contains conditionals, i would like to do: foo <- function(x,y){if (x<2) {return(0)} else {....} and data$c <- foo(data$a, data$b) But this gets me errors. What am i missing?

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2 回答 2

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您正在寻找ifelse功能。首先创建一个数据框：

> d <- data.frame(x = rnorm(5), y=rnorm(5))
> d
           x           y
1 -0.3581471  0.18149804
2  0.5096839  0.01260114
3  0.6742558  1.04851531
4  1.0761349 -0.17504221
5 -0.2373933 -1.11475886

现在使用创建一个额外的列ifelse：

> d$z <- ifelse(d$x < 0, 0, d$y + 1)
> d
           x           y         z
1 -0.3581471  0.18149804 0.0000000
2  0.5096839  0.01260114 1.0126011
3  0.6742558  1.04851531 2.0485153
4  1.0761349 -0.17504221 0.8249578
5 -0.2373933 -1.11475886 0.0000000
于 2012-06-22T10:59:28.413 回答
0 
df = data.frame(a=rnorm(20),b=runif(20))

new_var = function(x,y)
{
  if(x<0)
  { x = x^2}
  else
  { x = x^3}

  if(y<.5)
  { -log10(y)}
  else
  {
    exp(y)
  }
  return((2*(x+y))/x*y)
}

df$c = sapply(1:length(df$a), function(i){new_var(df$a[i],df$b[i])})

head(df)
            a          b          c
1 -0.09149107 0.04834675 0.65517298
2 -2.43732351 0.04086087 0.08228385
3 -1.69573283 0.54795413 1.30474339
4 -0.40106220 0.72952356 8.07641367
5 -0.38244706 0.65524147 7.18118555
6  0.76334945 0.38455655 1.43404971
于 2012-06-22T11:03:55.073 回答