copy result of unique() string vector in a dataframe R - r

Question

I am puzzled by something that I thought would easily work.
I have a dataframe with year, city, and species columns.
species City Year
80 Landpattedyr Sisimiut 2007
83 Landpattedyr Sisimiut 2008
87 Landpattedyr Sisimiut 2009
721733 Havpattedyr Upernavik 2010
721734 Havpattedyr Upernavik 2011
721735 Havpattedyr Upernavik 2007
I have used the function unique as follows
years<-unique(df$year)
city<-unique(df$City)
species<-unique(df$species)
now I need to assign a value in each of those vectors to a dataframe row based on an index, for example
hunting[1,]$year<-year[i]
hunting[1,]$group<-species[j]
hunting[1,]$city<-city[k]
The problem is that only year is copied properly while city and species in the hunting df show up as numbers. I can't figure out why this is happening. Can anybody help please?
year group city lat long total
1 2007 6 19 66.93 -53.66 4563
NA 2007 6 20 72.78 -56.15 91
3 2007 6 8 67.01 -50.72 388
4 2007 6 21 70.66 -52.12 280
5 2007 6 14 77.47 -69.23 469
6 2007 6 5 69.22 -51.10 1114

Answer 1

To find out if a column is factor or character you can use this is.factor(df$City) or is.character(df$City).
In the case of a factor column, the (unique) levels are stored in the levels attribute, which can be accessed with
levels(df$City)
Note: this may include levels that are not present in the vector, for instance, if some rows have been removed or if some levels have been added.
To retrieve the unique elements of a factoror character vector, you can use this:
as.character(unique(df$City))
Which will not return levels that are not present in factor columns.
Note: the last command is slightly more efficient than unique(as.character(df$City)), since the conversion is evaluated on a possibly shorter vector.