[R] looking for 'tied rows' in dataframe

[Ben Tupper]

Hi,

Might you replaced 'T' with a numeric value that signals the TRUE case without rumpling your matrix?  0 might be a good choice as it is never an index for a 1-based indexing system.

hold=apply(test,1,which.max)
hold[apply(test,1,isUnique)==FALSE] <- 0
hold
[1] 1 2 0
 


> On Mar 17, 2019, at 8:17 PM, Evan Cooch <evan.cooch using gmail.com> wrote:
> 
> Solved --
> 
> hold=apply(test,1,which.max)
>     hold[apply(test,1,isUnique)==FALSE] <- 'T'
> 
> Now, all I need to do is figure out how to get <- 'T' from turning everything in the matrix to a string.
> 
> 
> On 3/17/2019 8:00 PM, Evan Cooch wrote:
>> Got relatively close - below:
>> 
>> On 3/17/2019 7:39 PM, Evan Cooch wrote:
>>> Suppose I have the following sort of structure:
>>> 
>>> test <- matrix(c(2,1,1,2,2,2),3,2,byrow=T)
>>> 
>>> What I need to be able to do is (i) find the maximum value for each row, (ii) find the column containing the max, but (iii) if the maximum value is a tie (in this case, all numbers of the row are the same value), then I want which.max (presumably, a tweaked version of what which.max does) to reurn a T for the row where all values are the same.
>>> 
>>> Parts (i) and (ii) seem easy enough:
>>> 
>>> apply(test,1,max)  --- gives me the maximum values
>>> apply(test,1,which.max) --- gives me the column
>>> 
>>> But, standard which.max doesn't handles ties/duplicates in a way that serves my need. It defaults to returning the first column containing the maximum value.
>>> 
>>> What I'd like to end up with is, ultimately, something where apply(test,1,which.max) yields 1,2,T  (rather than 1,2,1).
>>> 
>>> So, a function which does what which.max currently does if the elements of the row differ, but which returns a T (or some such) if in fact the row values are all the same.
>>> 
>>> I've tried a bunch of things, to know avail. Closest I got was to use a function to test for whether or not a vector
>>> 
>>> isUnique <- function(vector){
>>>                  return(!any(duplicated(vector)))
>>>             }
>>> 
>>> which returns TRUE if values of vector all unique. So
>>> 
>>> apply(test,1,isUnique)
>>> 
>>> returns
>>> 
>>> [1]  TRUE  TRUE FALSE
>>> 
>>> but I'm stuck beyond this. 
>> 
>> The following gets me pretty close,
>> 
>> test_new <- test
>> test_new[which(apply(test,1,isUnique)==FALSE),] <- 'T'
>> 
>> but is clunky.
>> 
>> 
>> 
>> 
>> 
>> 
> 
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
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Ecological Forecasting: https://eco.bigelow.org/