问题
Many thanks for reading. Apologies for what I'm sure is a simple task.
I have a dataframe: (Edited: Added extra column not to be included in comparison)
b = c(5, 6, 7, 8, 10, 11)
c = c('david','alan','pete', 'ben', 'richard', 'edd')
d = c('alex','edd','ben','pete','raymond', 'alan')
df = data.frame(b, c, d)
df
b c d
1 5 david alex
2 6 alan edd
3 7 pete ben
4 8 ben pete
5 10 richard raymond
6 11 edd alan
I want to compare the group of columns c and d with the group of columns d and c. That is, for one row, I want to compare the combined values in c and d with the combined values in d and c for all other rows.
(Note the values could either be characters or integers)
Where these match I want to return the index of those rows which match, preferably as a list of lists. I need to be able to access the indexes without referring to the values in column c or d.
I.e. for the above dataframe, my expected output would be:
c(c(2, 6), c(3, 4))
((2,6), (3,4))
As:
Row 2: (c + d == alan + edd) = row 6: (d + c == edd + alan)
Row 3: (c + d == pete + ben) = row 4: (d + c == ben + pete)
I understand how to determine the match case for two separate columns using match melt, but not if they are joined together and iterating over all possible row combinations.
I envision something like:
lapply(1:6, function(x), ifelse((df$a & df$b) == (df$b & df$a), index(x), 0))
But obviously that is incorrect and won't work.
I consulted the following questions but have been unable to formulate an answer. I have no idea where to begin.
Matching multiple columns on different data frames and getting other column as result
match two columns with two other columns
Comparing two columns in a data frame across many rows
R Comparing each value of all pairs of columns
How can I achieve the above?
回答1:
You could do something like this. It splits the row indices 1:nrow(df) according to unique sorted strings formed from the columns of df. The sorting ensures that A,B and B,A are treated identically.
duplist <- split(1:nrow(df),apply(df,1,function(r) paste(sort(r),collapse=" ")))
duplist
$`alan edd`
[1] 2 6
$`alex david`
[1] 1
$`ben pete`
[1] 3 4
$`raymond richard`
[1] 5
来源：https://stackoverflow.com/questions/44132862/compare-group-of-two-columns-and-return-index-matches-r