禁止将大输出输出到R控制台

Question

How can I make R check whether an object is too large to print in the console? "Too large" here means larger than a user-defined value.

Example: You have a list f_data with two elements f_data$data (a 100MB data.frame) and f_data$info (for instance, a vector). Assume you want to inspect the first few entries of the f_data$data data.frame but you make a mistake and type head(f_data) instead of head(f_data$data) . R will try to print the whole content of f_data to the console (which would take forever). Is there somewhere an option that I can set in order to suppress the output of objects that are larger than let's say 1MB?

Edit: Thank you guys for your help. After implementing the max.rows option I realized that this gives indeed the desired output. BUT the problem that the output takes very long to show up still persists. I will give you a proper example below.

df_nrow=100000
df_ncol=100
#create list with first element being a large data.frame
#second element is a short vector
test_list=list(df=data.frame(matrix(rnorm(df_nrow*df_ncol),nrow=df_nrow,ncol=df_ncol)),
               vec=1:110)

#only print the first 100 elements of an object
options(max.print=100)

#head correctly displays the first row of the data.frame
#BUT for some reason the output takes really long to show up in the console (~30sec)
head(test_list)
#let's try to see how long exactly
system.time(head(test_list))
#   user  system elapsed 
#      0       0       0
#well, obviously system.time is not the proper tool to measure this

#the same problem if I just print the object to the console without using head
test_list$df

I assume that R performs some sort of analysis on the object being printed and this is what takes so long.

Edit 2: As per my comment below, I checked whether the problem persists if I use a matrix instead of a data.frame .

#create list with first element being a large MATRIX
test_list=list(mat=matrix(rnorm(df_nrow*df_ncol),nrow=df_nrow,ncol=df_ncol),vec=1:110)

#no problem
head(test_list)

#no problem
test_list$mat

Could it be that the output to the console is not really efficiently implemented for data.frame objects?

Answer 1

I think there is no such option, but you can check the size of an object with object.size and print it if is lower than a threshold (measure in bytes), for example:

print.small.objects <- function(x, threshold = 1e06, ...)
{
  if (object.size(x) < threshold) {
    print(x, ...)
  } else {
    cat(paste("too big object\n"))
    print(object.size(x))
  }
}

Answer 2

Here's an example that you could adjust up to 100MB. It basically only prints the first 6 rows and 5 columns if the object's size is above 8e5 bytes. You could also turn this into a function and place it in your .Rprofile

> lst <- list(data.frame(replicate(100, rnorm(1000))), 1:10)
> sapply(lst, object.size)
# [1] 810968     88
> lapply(lst, function(x){
      if(object.size(x) > 8e5) head(x)[1:5] else x
  })
#[[1]]
#          X1         X2          X3          X4         X5
#1  0.3398235 -1.7290077 -0.35367971  0.09874918 -0.8562069
#2  0.2318548 -0.3415523 -0.38346083 -0.08333569 -1.1091982
#3  0.0714407 -1.4561768  0.50131914 -0.54899188  0.1652095
#4 -0.5170228  1.7343073 -0.05602883  0.87855313  0.4025590
#5  0.6962212 -0.3179930  0.28016057  1.05414456 -0.5172885
#6  0.9471200  1.4424843 -1.46323827 -0.78004192 -1.3611820
#
#[[2]]
# [1]  1  2  3  4  5  6  7  8  9 10