Get column index from label in a data frame

Question

Say we have the following data frame    gt  df   A B C 1 1 2 3 2 4 5 6 3 7 8 9   We can select column  B  from its index    gt  df  2   1  2 5 8   Is there a way to get the index  2  from the column label   B

User · Answer

match  B   names df     Can work also if you have a vector of names

User · Answer

I wanted to see all the indices for the colnames because I needed to do a complicated column rearrangement  so I printed the colnames as a dataframe   The rownames are the indices   as data frame colnames df    1 A 2 B 3 C

User · Answer

This seems to be an efficient way to list vars with column number   cbind names df      Output          1   1    A    2    B    3    C     Sometimes I like to copy variables with position into my code so I use this function   varnums lt - function x   w as data frame c 1 length colnames x               paste0      colnames x    names w   c    Var Pos   w  varnums df    Output     Var Pos   A         1   B         2   C         3

User · Answer

The following will do it   which colnames df    B

User · Answer

you can get the index via grep and colnames   grep  B   colnames df    1  2   or use   grep   B    colnames df    1  2   to only get the columns called  B  without those who contain a B e g   ABC

User · Answer

Following on from chimeric s answer above    To get ALL the column indices in the df  so i used   which  names df  in c       or store in a list   indexLst lt -which  names df  in c

User · Answer

Use t function   t colnames df           1      2      3      4      5      6     1    var1   var2   var3   var4   var5   var6

User · Answer

Here is an answer that will generalize Henrik s answer  df data frame A rnorm 100   B rnorm 100   C rnorm 100   numeric columns lt -c  A    B    C   numeric index lt -sapply 1 length numeric columns   function i  grep numeric columns i   colnames df

[r] Get column index from label in a data frame

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