Calculate row means on subset of columns

Question

Given a sample data frame   C1 lt -c 3 2 4 4 5  C2 lt -c 3 7 3 4 5  C3 lt -c 5 4 3 6 3  DF lt -data frame ID c  A   B   C   D   E   C1 C1 C2 C2 C3 C3   DF     ID C1 C2 C3   1  A  3  3  5   2  B  2  7  4   3  C  4  3  3   4  D  4  4  6   5  E  5  5  3   What is the best way to create a second data frame that would contain the ID column and the mean of each row  Something like this   ID  Mean A    3 66 B    4 33 C    3 33 D    4 66 E    4 33   Something similar to    RM lt -rowMeans DF  2 4     I d like to keep the means aligned with their ID s

User · Answer

Using dplyr   library dplyr     exclude ID column then get mean DF   gt     transmute ID              Mean   rowMeans select    -ID      Or    select the columns to include in mean DF   gt     transmute ID              Mean   rowMeans select    C1 C3         ID     Mean   1  A 3 666667   2  B 4 333333   3  C 3 333333   4  D 4 666667   5  E 4 333333

User · Answer

rowMeans is nice  but if you are still trying to wrap your head around the apply family of functions  this is a good opprotunity to begin understanding it  DF  Mean    lt - apply DF  2 4   1  mean   Notice I m doing a slightly different assignment than the first example  This approach makes it easier to incorporate it into for loops

User · Answer

You can create a new row with   in your data frame corresponding to the Means  DF Mean  lt - rowMeans DF  2 4

User · Answer

Another solution using pivot longer  amp  pivot wider from latest Tidyr update   You should try using pivot longer to get your data from wide to long form Read latest tidyR update on pivot longer  amp  pivot wider  https   tidyr tidyverse org articles pivot html   library tidyverse  C1 lt -c 3 2 4 4 5  C2 lt -c 3 7 3 4 5  C3 lt -c 5 4 3 6 3  DF lt -data frame ID c  A   B   C   D   E   C1 C1 C2 C2 C3 C3    Output here     ID     mean    lt fct gt   lt dbl gt  1 A      3 67 2 B      4 33 3 C      3 33 4 D      4 67 5 E      4 33

User · Answer

Calculate row means on a subset of columns   Create a new data frame which specifies the first column from DF as an column called ID and calculates the mean of all the other fields on that row  and puts that into column entitled  Means     data frame ID DF  1   Means rowMeans DF  -1      ID    Means 1  A 3 666667 2  B 4 333333 3  C 3 333333 4  D 4 666667 5  E 4 333333

User · Answer

Starting with your data frame DF  you could use the data table package   library data table      EDIT  As suggested by  MichaelChirico  setDT converts a    data frame to a data table by reference and is preferred    if you don t mind losing the data frame setDT DF     EDIT  To get the column name  Mean    DF     Mean   rowMeans  SD    by   ID          ID     Mean    1    A 3 666667    2    B 4 333333    3    C 3 333333    4    D 4 666667    5    E 4 333333

[r] Calculate row means on subset of columns

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