CODEWITHSUNDEEP
rloops
pyll
pyll

Reputation: 1754

Loop through vector of variables

I have a process that I'd like to loop through one variable at a time.

Although my process is much more complicated, I've used the below to illustrate the basic problem.

Suppose I want to build a histogram and do lots of other stuff for each variable in iris. The following accomplishes that goal:

hist(iris$Sepal.Length, main = paste("Histogram of Sepal.Length"))
hist(iris$Sepal.Width, main = paste("Histogram of Sepal.Width"))
hist(iris$Petal.Length, main = paste("Histogram of Petal.Length"))
hist(iris$Petal.Width, main = paste("Histogram of Petal.Width"))

However, my data frame is much larger, and my process much more complex. I'd like to wrap this in a loop like below (this does not work, but is how I'm envisioning in my head).

name.list <- names(iris)

for (i in 1:4) {

  print(i)
  print(name.list[i])
  print(paste0('iris$', name.list[i]))

  hist(paste0('iris$', name.list[i]), main = paste("Histogram of ", name.list[i]))

  # A bunch of other stuff I need to do with this variable
  # ...
  # ...

}

What am I missing here? How can I wrap this code to loop through one at a time?

Upvotes: 2

Views: 2843

Answers (1)

Joris Meys
Joris Meys

Reputation: 108613

It's easier if you treat a data.frame as a list. An object of class data.frame is a list, so you can use the list selection [[ here:

for( i in names(iris)){
  tmp <- iris[[i]]
  if(is.numeric(tmp))
    hist(tmp, main = paste("Histogram of",i))
}

See also the answers to this question : Pass a data.frame column name to a function

Upvotes: 3

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