[R] looking for 'tied rows' in dataframe

[Evan Cooch]

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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