Multiple files, grep value, create new column with value and bind data

Question

[odayel]

Hello! Thank you for your help in advance. I'm still getting my bearings with R and I am rubbish with loops

I have 1200 .txt files where the top 15 lines contain meta data, the bottom data contain the data readout (varying rows with 7 variables). I want to pull the "mac value" (row 9, column 2) from the top 15 lines and repeat that value in a new column with the other values of the data. I want to repeat this process for all 1200 sample files and then bind all the rows together to have a Masterlist. Here's an example for 2 of the .txt files. Any suggestions as how to set this up for all 1200 files would be greatly appreciated!!! Thank you!

df=read.csv("sample1.txt", nrows=15, sep="\t")
 patb <- "mac*"
 b <- grep(patb, df[9,2], value = TRUE)

 df1=read_table("sample1.txt", skip = 15)
 df1$macid=rep(b, nrow(df1))

 df2=read.csv("sample2. txt", nrows=15, sep="\t")
 patb <- "mac*"
 b2 <- grep(patb, df2[9,2], value = TRUE)

 df3=read_table("sample2.txt", skip = 15)
 df3$macid=rep(b2, nrow(df3))

 Master=rbind(df1, df3)

Answer 1

[ddiez]

Something like this should work (WARNING: untested; might need some adjustments):

# put all your file names into a character vector.
# adjust `path` and `pattern` to ensure you pick the right ones.
ff <- list.files(path = ".", pattern = ".txt")

# iterate over the file names. `f` contains the name of one
# file in each iteration. `lapply` returns a list.
master <- lapply(ff, funtion(f) {
  # read the 9th row, 2nd column. 
  mac_id <- read.table(f, skip = 8, nrows = 1)[, 2]
  # read the rest.
  tmp <- read.table(f, skip = 15)
 # join columns.
  cbind(tmp, rep(mac_id, nrow(tmp))
})
# master is now a list of 1-row data.frames of same dimensions.
# this puts them together:
master <- do.call(rbind, master)

If your data files has some inconsistencies regarding the position of mac value then you can get around that using grep and alike.

[odayel]

and @ddiez you are a rockstar yet again! Thanks this is working now and I was able to implement grep for inconsistencies. Thank you!!