22015-03-15 11:06:03mandy.vogel@googlemail.com12015-03-15 11:04:41mandy.vogel@googlemail.com

rbind() can be used to combine two dataframes (or matrices) in the sense of adding rows, the column names and types must be the same for the two objects ]]> ]]> ]]>

cbind() can be used to combine two dataframes (or matrices) in the sense of adding columns, the number of rows must be the same for the two objects ]]> it is not recommended to use cbind() to combining data frames

merge() is the command of choice for merging or joining data frames it is the equivalent of join in sql there are four cases inner join left outer join right outer join full outer join (]]> (]]>

inner join means: keep only the cases present in both of the data frames ]]>

left outer join means: keep all cases of the left data frame no matter if they are present in the right data frame (all.x=T) ]]>

right outer join means: keep all cases of the right data frame no matter if they are present in the left data frame (all.y=T) ]]>

full outer join means: keep all cases of both data frames (all=T) ]]> if not stated otherwise R uses the intersect of the names of both data frames, in our case only \textit{id} you can specify these columns directly by \texttt{by=c("colname1","colname2")} if the columns are named identical or using\\ \texttt{by.x=c("colname1.x","colname2.x"),

now read in the file personendaten.txt using the appropriate command join the demographics with our pre1 data frame (even though it does not make sense now)

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