#setting package and directory
library(plyr)
library(stringr)
setwd("/Users/macbook/Desktop/Project_Folder/File_folder1")

#Creating a list of all the filenames:
filenames <- list.files(path = "/Users/macbook/Desktop/Project_Folder/File_folder1")

#creating a function to read csv and in the same time adding an additional column with the name of the file
read_csv_filename <- function(filename)
  {
  ret <- read.csv(filename, header=TRUE, sep=",")
  ret$Source <- filename #EDIT
  ret
}

#importing
import <- ldply(filenames, read_csv_filename)

#making a copy of import
data<-import

#modifying the file name so it removes ".csv" and change the header
data$Source<-str_sub(data$Source, end=-5)
data[1,3]<-"date_expnb_pulsenb"
t<-substr(data[1,3],1,3)
head(data, n=10)

#create a column with the experiment number, extracted from the file name
data$expnb<-substr(data$Source, 10, 13)
data$expnb<-as.numeric(data$expnb)
head(data, n=10)
tail(data, n=10)

> head(data, n=10)
           Time   Channel.A            Source pulsenb expnb
1          (us)         (A)     expnb_pulsenb      NA    NA
2  -20.00200030 -0.29219970 20190409-0001_002       2     1
3  -20.00100030 -0.29219970 20190409-0001_002       2     1

> tail(data, n=10)
                 Time   Channel.A            Source pulsenb expnb
20800511 179.99199405 -0.81815930 20190409-0001_105     105     1
20800512 179.99299405 -0.81815930 20190409-0001_105     105     1