[R] Read a list of files into named R data.frames

[David Winsemius]

On Sep 9, 2011, at 10:39 AM, Michael Friendly wrote:

> I have a collection of .csv files in a directory, and want to read  
> them into R data.frames whose names
> are the same as the file names, without the .csv extension
>
> e.g., from
> > (files <- list.files(pattern="*.csv"))
> [1] "Allstar.csv"             "AllstarFull.csv"
> [3] "Appearances.csv"         "AwardsManagers.csv"
> [5] "AwardsPlayers.csv"       "AwardsShareManagers.csv"
> [7] "AwardsSharePlayers.csv"  "Batting.csv"
> [9] "BattingPost.csv"         "Fielding.csv"
> [11] "FieldingOF.csv"          "FieldingPost.csv"
> [13] "HallOfFame.csv"          "HOFold.csv"
> [15] "Managers.csv"            "ManagersHalf.csv"
> [17] "Master.csv"              "Pitching.csv"
> [19] "PitchingPost.csv"        "Salaries.csv"
> [21] "Schools.csv"             "SchoolsPlayers.csv"
> [23] "SeriesPost.csv"          "Teams.csv"
> [25] "TeamsFranchises.csv"     "TeamsHalf.csv"
>
> > Allstar <- read.csv("Allstar.csv", header=TRUE)
>  ...
> > TeamsHalf <- read.csv("TeamsHalf.csv", header=TRUE)
>
> Below is what I tried, which reads all the files, but doesn't create  
> the R objects in the global environment.
> What is missing here?
>
> for (i in 1:length(files)) {
>    inp <- read.csv(file=files[i], header=TRUE)
>    name <- sub(".csv", "", files[i])
>    cat("Read ", files[i], "\trows: ", nrow(inp), " cols: ",  
> ncol(inp), "\n")

Generally the assign function is used to create objects with a  
particular name. If you wanted to use eval then the text needs to be  
passed through parse() before being given to eval, but that is not the  
preferred method.

Perhaps:

      assign( files[i], inp)

Inside a for loop I think that gets done in the calling environment  
but if you were in a function  you would need to use the environment  
argument to get it to "stick".


>    eval(paste(name, "<- inp"))
> }
>
> Read  Allstar.csv       rows:  4475  cols:  3
> Read  AllstarFull.csv   rows:  4676  cols:  8
> Read  Appearances.csv   rows:  94157  cols:  20
> Read  AwardsManagers.csv        rows:  57  cols:  6
> Read  AwardsPlayers.csv         rows:  2679  cols:  6
> Read  AwardsShareManagers.csv   rows:  344  cols:  7
> Read  AwardsSharePlayers.csv    rows:  6354  cols:  7
> Read  Batting.csv       rows:  93955  cols:  24
> Read  BattingPost.csv   rows:  9840  cols:  22
> Read  Fielding.csv      rows:  160710  cols:  18
> Read  FieldingOF.csv    rows:  12028  cols:  6
> Read  FieldingPost.csv  rows:  10458  cols:  17
> Read  HallOfFame.csv    rows:  3913  cols:  8
> Read  HOFold.csv        rows:  289  cols:  7
> Read  Managers.csv      rows:  3238  cols:  10
> Read  ManagersHalf.csv  rows:  93  cols:  10
> Read  Master.csv        rows:  17674  cols:  33
> Read  Pitching.csv      rows:  40432  cols:  30
> Read  PitchingPost.csv  rows:  4284  cols:  30
> Read  Salaries.csv      rows:  21464  cols:  5
> Read  Schools.csv       rows:  749  cols:  5
> Read  SchoolsPlayers.csv        rows:  6147  cols:  4
> Read  SeriesPost.csv    rows:  256  cols:  9
> Read  Teams.csv         rows:  2655  cols:  48
> Read  TeamsFranchises.csv       rows:  120  cols:  4
> Read  TeamsHalf.csv     rows:  52  cols:  10
> Read  Xref_Stats.csv    rows:  2753  cols:  3
> > ls()
> [1] "files" "i"     "inp"   "name"
> >
>
> -- 
> Michael Friendly     Email: friendly AT yorku DOT ca
> Professor, Psychology Dept.
> York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
> 4700 Keele Street    Web:   http://www.datavis.ca
> Toronto, ONT  M3J 1P3 CANADA
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT