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

[Michael Friendly]

Thanks, David & Jean

assign(), as you suggested works to create the named objects in the 
global environment.

In my application, I also want to :
(a) save each object to a similarly-named .RData file with that object
(b) create a corresponding .Rd documentation file.

(b) works fine in my loop below, but for (a) I'm unable to find a way to 
use save() so that the
saved .RData file contains the one data.frame of the same name.

The code below
does produce all the separate .RData files, but each one contains object 
called 'inp'
rather than the name of the object created by assign().  Using 
save(name, file=...)
below produces similar .RData files with one object called 'name'.

#setwd("c:/sasuser/data/lahman")

# Read the Lahman MLB .csv files and create .Rdata and .Rd files
(files <- list.files(pattern="*.csv"))

for (i in 1:length(files)) {
     inp <- read.csv(file=files[i], header=TRUE)
     cname <- name <- sub(".csv", "", files[i])
     cat("Read:", files[i], "\trows: ", nrow(inp), " cols: ", ncol(inp), 
"\n")
     assign( name, inp)
     save(inp, file=paste(cname, ".RData", sep=""))
     promptData(inp, name=cname)
}

To get what I want for (a), I can save() each separately, as in

save(Allstar,             file="Allstar.RData")
save(AllstarFull,         file="AllstarFull.RData")
save(Appearances,         file="Appearances.RData")
...

Is there some special incantation for the name of the saved object in a 
loop that I've missed?

TIA
-Michael


On 9/9/2011 10:51 AM, David Winsemius wrote:
>
> 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
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>


-- 
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