[R] print only a few lines of an object

[John Fox]

Dear Jeff,

On 2022-03-23 3:36 p.m., Jeff Newmiller wrote:
> After-thought...
> 
> Why not just use head() and tail() like normal R users do?

head() and tail() are reasonable choices if there are many rows, but not 
if there are many columns.

My first thought was your previous suggestion to redefine print() 
methods (although I agree with you that this isn't a good idea), but 
though I could get that to work for data frames, I couldn't for matrices.

Adapting my preceding examples using car::brief():

 > X <- matrix(rnorm(20000*200), nrow = 20000)

 > library("car")
Loading required package: carData

 > print.data.frame <- function(x, ...){ # not recommended!
+   brief(x, ...)
+   invisible(x)
+ }

 > as.data.frame(X)
20000 x 200 data.frame (19995 rows and 195 columns omitted)
               V1         V2         V3 . . .        V199       V200
              [n]        [n]        [n]               [n]        [n]
1     -1.1810658 -0.6090037  1.0057908        1.23860428  0.6265465
2     -1.6395909 -0.2828005 -0.6418150        1.12875894 -0.7594760
3      0.2751099  0.2268473  0.2267713        0.64305445  1.1951732
. . .
19999  1.2744054  1.0170934 -1.0172511       -0.02997537  0.7645707
20000 -0.4798590 -1.8248293 -1.4664622       -0.06359483  0.7671203


 > print.matrix <- function(x, ...){ # not recommended (and doesn't work)!
+   brief(x, ...)
+   invisible(x)
+ }

 > X
                   [,1]          [,2]          [,3]          [,4] 
   [,5]
     [1,] -1.181066e+00 -6.090037e-01  1.005791e+00  3.738742e+00 
-6.986169e-01
     [2,] -1.639591e+00 -2.828005e-01 -6.418150e-01 -7.424275e-01 
-1.415092e-01
     [3,]  2.751099e-01  2.268473e-01  2.267713e-01 -6.308073e-01 
7.042624e-01
     [4,] -9.210181e-01 -4.617637e-01  1.523291e+00  4.003071e-01 
-2.792705e-01
     [5,] -6.047414e-01  1.976075e-01  6.065795e-01 -8.074581e-01 
-4.089352e-01

. . . [many lines elided]

                 [,196]        [,197]        [,198]        [,199] 
[,200]
     [1,] -1.453015e+00  1.347678e+00  1.189217e+00  1.238604e+00 
0.6265465033
     [2,] -1.693822e+00  2.689917e-01 -1.703176e-01  1.128759e+00 
-0.7594760299
     [3,]  1.260585e-01  6.589839e-01 -7.928987e-01  6.430545e-01 
1.1951731814
     [4,] -1.890582e+00  7.614779e-01 -5.726204e-01  1.090881e+00 
0.9570510645
     [5,] -8.667687e-01  5.365750e-01 -2.079445e+00  1.209543e+00 
-0.2697400234
  [ reached getOption("max.print") -- omitted 19995 rows ]

So, something more complicated that I don't understand is going on with 
matrices.

Best,
  John

> 
> On March 23, 2022 12:31:46 PM PDT, Jeff Newmiller <jdnewmil using dcn.davis.ca.us> wrote:
>> Sure. Re-define the print method for those objects. Can't say I recommend this, but it can be done.
>>
>> On March 23, 2022 11:44:01 AM PDT, Naresh Gurbuxani <naresh_gurbuxani using hotmail.com> wrote:
>>> In an R session, when I type the name of an object, R prints the entire object (for example, a 20000 x 5 data.frame).  Is it possible to change the default behavior so that only the first five and last five rows are printed?
>>>
>>> Similarly, if the object is a 20000 x 200 matrix, the default behavior will be to print first five and last five columns, combined with first five and last five rows.
>>>
>>> Thanks,
>>> Naresh
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>>
>