data frame Group By column

Question

I have a data frame DF   Say DF is     A B 1 1 2 2 1 3 3 2 3 4 3 5 5 3 6    Now I want to combine together the rows by the column A and to have the sum of the column B   For example     A B 1 1 5 2 2 3 3 3 11   I am doing this currently using an SQL query with the sqldf function  But for some reason it is very slow  Is there any more convenient way to do that  I could do it manually too using a for loop but it is again slow  My SQL query is   Select A Count B  from DF group by A     In general whenever I don t use vectorized operations and I use for loops the performance is extremely slow even for single procedures

User · Answer

require reshape2   T  lt - melt df  id   c  A     T  lt - dcast T  A   variable  sum    I am not certain the exact advantages over aggregate

User · Answer

This is a common question  In base  the option you re looking for is aggregate  Assuming your data frame is called  mydf   you can use the following    gt  aggregate B   A  mydf  sum    A  B 1 1  5 2 2  3 3 3 11   I would also recommend looking into the  data table  package    gt  library data table   gt  DT  lt - data table mydf   gt  DT   sum B   by   A     A V1 1  1  5 2  2  3 3  3 11

User · Answer

I would recommend having a look at the plyr package  It might not be as fast as data table or other packages  but it is quite instructive  especially when starting with R and having to do some data manipulation    gt  DF  lt - data frame A   c  1    1    2    3    3    B   c 2  3  3  5  6    gt  library plyr   gt  DF sum  lt - ddply DF  c  A    summarize  B   sum B    gt  DF sum   A  B 1 1  5 2 2  3 3 3 11

User · Answer

Using dplyr   require dplyr      df  lt - data frame A   c 1  1  2  3  3   B   c 2  3  3  5  6   df   gt   group by A    gt   summarise B   sum B       Source  local data frame  3 x 2           A  B    1 1  5    2 2  3    3 3 11   With sqldf   library sqldf  sqldf  SELECT A  SUM B  AS B FROM df GROUP BY A

[r] data.frame Group By column

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