read CSV file Until...

Hi All,
I'm using read_CSV2 to read CSV files, with the same structures, but I would like to read them until a certain row (which varie according to the CSV):
row_2 <- 24
row_3 <- 21
info2 <- read_csv2(data2,
skip=2)[ ,c(1:2, 12:14)] #select columns 1to2 and then 12 to 14

info3 <- read_csv2(data3,
skip=2)[ ,c(1:2, 12:14)]

Here I would like to do 2 things:

  • Create a macro to automatize my read CSV.
  • And create a macro variable to read the CSV file until the appropriate row.

But I don't know how to catch the right row number automatically.

Basically, the appropriate row would be the row number x where the 1st column contains the 1st 'Total' word. Or also another way would be to select all the rows until the next empty row ...
Does someone knows how I can select and get the row number ?

Unless the files are very large, I would read in the entire file and make a subset afterward.

DF <- read.csv2("/home/fjcc/R/Play/Dummy.csv")
#>    Name Value
#> 1     A     2
#> 2     B     4
#> 3     C     6
#> 4 Total    12
#> 5     F     4
#> 6     g     6
#> 7     q    23
#> 8 Total    33
Totals <- which(DF$Name == "Total")
DF2 <- DF[1:Totals[1], ]
#>    Name Value
#> 1     A     2
#> 2     B     4
#> 3     C     6
#> 4 Total    12

Created on 2019-10-07 by the reprex package (v0.2.1)



I agree that @FJCC option is the one you should implement in case the files are small given it guarantees the best performance.

If however the files are too large to read all at once, you can use something like this

filePath = "data.csv"
separator = ","
hasHeader = T
rowStart = 1
rowEnd = 20

myData = scan(filePath, "character", skip = rowStart + hasHeader - 1, nlines = rowEnd - rowStart + 1)
myData = purrr::map_df(1:length(myData), function(x){
  data.frame(t(unlist(strsplit(myData[x], split = separator))), stringsAsFactors = F)
}) %>% readr::type_convert()

  colnames(myData) = unlist(strsplit(scan(filePath, "character", nlines = 1), split = ","))

  • The scan function will read any file's lines. The skip and nlines arguments let you decide which lines to read in
  • Since you read the lines as a string, you need to split the string according to the separator the file has (this example comma)
  • After splitting you merge all into a data frame and use the type_convert to guess the column class
  • Depending on a header or not, you assign the column names in the end

The final result is the first 20 lines of the data file, in this case with header (so 21 lines in total were read)

Hope this helps,

1 Like


It works TipTop

Thank you :slight_smile:

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