Merging every three columns of a data frame in R-CodePudding

I have data frame contain around 900 columns and I want to combine the content of every 3 columns in one column I tried to do a loop but I'm not good at it, can you please help me?
the data frame look like this :

df_out <- data.frame(
  "name" = c("1", "2", "3", "4", "5", "6", "7", "8"),
  "col1"=rep("B",times= 8),
  "col2"=rep("A",times= 8),
  "col3"=rep("G",times= 8),
  "col4"=rep("C",times= 8),
  "col5"=rep("C",times=8),
  "col6"=rep("B",times= 8),
  "col7"=rep("A",times= 8),
  "col8"=rep("G",times= 8),
  "col9"=rep("C",times= 8),
  "col10"=rep("C",times=8),
  "col11"=rep("B",times= 8),
  "col12"=rep("A",times= 8),
  "col13"=rep("G",times= 8),
  "col14"=rep("C",times= 8),
  "col15"=rep("C",times=8)  
)

df_out

So the final results should be like this:

df_out2 <- data.frame(
  "name" = c("1", "2", "3", "4", "5", "6", "7", "8"),
  "col1"=rep("BAG",times= 8),
  "col2"=rep("CCB",times= 8),
  "col3"=rep("AGC",times= 8),
  "col4"=rep("CBA",times= 8),
  "col5"=rep("GCC",times=8))

df_out2

Any help is appreciated. Also, Can you please recommend any book or good website to learn loops in R? Thank you

CodePudding user response：

Please find below one possible solution using tidyr and dplyr libraries.

Reprex

Code

library(tidyr)
library(dplyr)

cnames <- paste0("col", 1:((ncol(df_out)-1)/3))  
separators <- seq(from = 3, to = (ncol(df_out)-1)-3, by = 3)

df_out %>% 
  select(-name) %>% 
  unite(newCol, "col1":"col15", sep = "") %>% # for your case, please change "col1":"col15" to "col1":"col900"
  separate(newCol, into = cnames, sep = separators) %>% 
  cbind(df_out[1], .)

Output

#>   name col1 col2 col3 col4 col5
#> 1    1  BAG  CCB  AGC  CBA  GCC
#> 2    2  BAG  CCB  AGC  CBA  GCC
#> 3    3  BAG  CCB  AGC  CBA  GCC
#> 4    4  BAG  CCB  AGC  CBA  GCC
#> 5    5  BAG  CCB  AGC  CBA  GCC
#> 6    6  BAG  CCB  AGC  CBA  GCC
#> 7    7  BAG  CCB  AGC  CBA  GCC
#> 8    8  BAG  CCB  AGC  CBA  GCC

^{Created on 2022-02-20 by the reprex package (v2.0.1)}

CodePudding user response：

Base R option.

Using split.default we can split the dataframe into 3 columns each, use do.call with paste0 to combine the values together for each row.

n <- 3
tmp <- df_out[-1]

cbind(df_out[1], 
      sapply(split.default(tmp, ceiling(seq_along(tmp)/n)), 
             function(x) do.call(paste0, x)))

#  name   1   2   3   4   5
#1    1 BAG CCB AGC CBA GCC
#2    2 BAG CCB AGC CBA GCC
#3    3 BAG CCB AGC CBA GCC
#4    4 BAG CCB AGC CBA GCC
#5    5 BAG CCB AGC CBA GCC
#6    6 BAG CCB AGC CBA GCC
#7    7 BAG CCB AGC CBA GCC
#8    8 BAG CCB AGC CBA GCC