Extracting specific columns from a data frame

Question

I have an R data frame with 6 columns  and I want to create a new dataframe that only has three of the columns   Assuming my data frame is df  and I want to extract columns A  B  and E  this is the only command I can figure out    data frame df A df B df E    Is there a more compact way of doing this

User · Answer

For some reason only  df    names df   in  c  A   B   E       worked for me  All of the above syntaxes yielded  undefined columns selected

User · Answer

You can subset using a vector of column names  I strongly prefer this approach over those that treat column names as if they are object names  e g  subset     especially when programming in functions  packages  or applications    data for reproducible example    and to avoid confusion from trying to subset  stats  df   df  lt - setNames data frame as list 1 5    LETTERS 1 5     subset df c  quot A quot   quot B quot   quot E quot     Note there s no comma  i e  it s not df  c  quot A quot   quot B quot   quot C quot      That s because df   quot A quot   returns a vector  not a data frame  But df  quot A quot   will always return a data frame  str df  quot A quot        data frame      1 obs  of  1 variable       A  int 1 str df   quot A quot       vector     int 1   Thanks to David Dorchies for pointing out that df   quot A quot   returns a vector instead of a data frame  and to Antoine Fabri for suggesting a better alternative  above  to my original solution  below     subset  original solution--not recommended  df  c  quot A quot   quot B quot   quot E quot       returns a data frame df   quot A quot                 returns a vector

User · Answer

Using the dplyr package  if your data frame is called df1   library dplyr   df1   gt     select A  B  E    This can also be written without the   gt   pipe as   select df1  A  B  E

User · Answer

Where df1 is your original data frame   df2  lt - subset df1  select   c 1  2  5

User · Answer

You can also use the sqldf package which performs selects on R data frames as    df1  lt - sqldf  select A  B  E from df     This gives as the output a data frame df1 with columns  A  B  E

User · Answer

and subset are not substitutable     does return a vector if only one column is selected   df   data frame a  a  b  b        identical    df  c  a        subset df select  a       identical    df  c  a   b         subset df select c  a   b

User · Answer

This is the role of the subset   function    gt  dat  lt - data frame A c 1 2  B c 3 4  C c 5 6  D c 7 7  E c 8 8  F c 9 9     gt  subset dat  select c  A    B      A B 1 1 3 2 2 4

User · Answer

You can use with     with df  data frame A  B  E

User · Answer

df lt - dplyr  select   df A B C    Also  you can assign a different name to the newly created data  data lt - dplyr  select   df A B C

User · Answer

There are two obvious choices   Joshua Ulrich s df  c  A   B   E    or   df  c 1 2 5     as in    gt  df  lt - data frame A c 1 2  B c 3 4  C c 5 6  D c 7 7  E c 8 8  F c 9 9     gt  df   A B C D E F 1 1 3 5 7 8 9 2 2 4 6 7 8 9  gt  df  c 1 2 5     A B E 1 1 3 8 2 2 4 8  gt  df  c  A   B   E      A B E 1 1 3 8 2 2 4 8

[r] Extracting specific columns from a data frame

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