Finding the index or unique values from a dataframe column

Question

I have a dataframe

TableName Function Argument
A         func1    3
B         func1    4
A         func2    6
B         func2    2
C         func1    5
         


        

Answer 1

I'd suggest to use either simply

(vec <- tapply(df$Argument, df$TableName, FUN = `identity`))
# $A
# [1] 3 6
#
# $B
# [1] 4 2
#
# $C
# [1] 5

or

(dfNew <- data.frame(TableName = unique(df$TableName), Index = vec))
#   TableName Index
# A         A  3, 6
# B         B  4, 2
# C         C     5

vec is a list (rather than a character with concatenated numbers) with easy access to names(vec) and, e.g.,

vec$A
# [1] 3 6

while dfNew is a data frame whose second column is also a list:

dfNew[2]
#   Index
# A  3, 6
# B  4, 2
# C     5

dfNew[,2]
# [[1]]
# [1] 3 6
#
# [[2]]
# [1] 4 2
#
# [[3]]
# [1] 5

dfNew[2]["A",][[1]]
# [1] 3 6

In this case, however, it's not so convenient to reach the indices by TableName, so I'd stick with vec.