CODEWITHSUNDEEP
r
Linda Espey
Linda Espey

Reputation: 145

create mean per row for every second column

So what I am trying to do is to create a mean for each row, but only including every second column. An example df would be:

C1<-c(3,2,4,4,5)
C2<-c(3,7,3,4,5)
C3<-c(5,4,3,6,3)
C4<-c(5,4,3,6,3)
C5<-c(5,6,3,6,2)
C6<-c(5,5,3,6,4)
C7<-c(5,6,3,6,1)
C8<-c(5,7,3,6,2)
DF<-data.frame(ID=c("A","B","C","D","E"),C1=C1,C2=C2,C3=C3, C4=C4, C5=C5, C6=C6, C7=C7, C8=C8)

 DF
  ID C1 C2 C3 C4 C5 C6 C7 C8
1  A  3  3  5  5  5  5  5  5
2  B  2  7  4  4  6  5  6  7
3  C  4  3  3  3  3  3  3  3
4  D  4  4  6  6  6  6  6  6
5  E  5  5  3  3  2  4  1  2

So now I would like to calculate the mean of C2, C4, C6 and C8 and add this as a new column in the df. What I tried is this:

DF$mean <- rowMeans(DF[seq(2, nrow(dat_all_b), 2),])

This is the error produced: "Fehler in $<-.data.frame(*tmp*, frequency_mean, value = c(350 = NA, : replacement has 14 rows, data has 30" Fehler = error

My actual df has way more columns and i want to calculate the mean across every second column. Expected output:

 DF
  ID C1 C2 C3 C4 C5 C6 C7 C8 mean_1
1  A  3  3  5  5  5  5  5  5   4,5
2  B  2  7  4  4  6  5  6  7   5,75
3  C  4  3  3  3  3  3  3  3    3
4  D  4  4  6  6  6  6  6  6    5,5
5  E  5  5  3  3  2  4  1  2   3,5

Any help will be appreciated!

Upvotes: 0

Views: 327

Answers (4)

uceslc0
uceslc0

Reputation: 81

I would suggest to look into the apply family. In this case, by using apply and set the margin to 1 (by row -- while setting it to 2 will give you the mean by column) will solve the issue.

DF$mean <- apply(DF[,2:ncol(DF)], 1, mean)

Please note, this is more flexible as you can also quickly adapt to a number of other cases. as an example, to get the maximum value by row you can apply the max function by row to your dataframe:

DF$max <- apply(DF[,2:ncol(DF)], 1, max)

Upvotes: 0

Joe
Joe

Reputation: 193

Here is a dplyr solution:

library(tidyverse)
DF %>% 
rowwise() %>%
mutate(mean = mean(c(C1, C2), na.rm=TRUE))

Upvotes: 1

AnilGoyal
AnilGoyal

Reputation: 26238

This will give you mean of every even numbered column if we leave ID column.

DF$mean_1 <- rowMeans(DF[(seq_along(DF)[(seq_along(DF) %% 2 == 1)])][-1])

  ID C1 C2 C3 C4 C5 C6 C7 C8 mean_1
1  A  3  3  5  5  5  5  5  5   4.50
2  B  2  7  4  4  6  5  6  7   5.75
3  C  4  3  3  3  3  3  3  3   3.00
4  D  4  4  6  6  6  6  6  6   5.50
5  E  5  5  3  3  2  4  1  2   3.50

Upvotes: 0

Ronak Shah
Ronak Shah

Reputation: 389275

You can use rowMeans for every 2nd column as :

DF$mean_1 <- rowMeans(DF[seq(3, ncol(DF), 2)], na.rm = TRUE)
DF

#  ID C1 C2 C3 C4 C5 C6 C7 C8 mean_1
#1  A  3  3  5  5  5  5  5  5   4.50
#2  B  2  7  4  4  6  5  6  7   5.75
#3  C  4  3  3  3  3  3  3  3   3.00
#4  D  4  4  6  6  6  6  6  6   5.50
#5  E  5  5  3  3  2  4  1  2   3.50

This gives mean of C2, C4, C6 and C8. I am not sure if you need another column called mean_2 which would be mean of C1, C3, C5 and C7 ?

Upvotes: 0

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