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Reading from a specific file from a directory containing many files in hadoop


Reading from a specific file from a directory containing many files in hadoop

By : Chinmay Raote
Date : November 18 2020, 11:13 AM
this will help You need to write a custom PathFilter implementation and then use setInputPathFilter on FileInputFormat in your driver code. Please take a look at the below link:
https://hadoopi.wordpress.com/2013/07/29/hadoop-filter-input-files-used-for-mapreduce/
code :


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Reading multiple files in a directory starting from a specific row

Reading multiple files in a directory starting from a specific row


By : Fred Hawk
Date : March 29 2020, 07:55 AM
help you fix your problem In addition to @James's answer, using lapply only reads the files into a list, not into a common data.frame. From your question it is not obvious if you want this. But I'll add it for completeness sake anyway.
To be able to identify to which file a row in the common data.frame belonged originally, I often add a column with the filename. In pseudo-code this would look something like:
code :
files = list.files()
data_list = lapply(files, function(f) {
     dat = read.csv(fname, skip = 6)
     dat$fname = fname
     return(dat)
   })
data_df = do.call("rbind", data_list)
library(plyr)
files = list.files()
data_df = ldply(files, read.csv, skip = 6)
Reading directory using file api : how to handle a directory containing 20000-30000 files?

Reading directory using file api : how to handle a directory containing 20000-30000 files?


By : Sahil Vashisht
Date : March 29 2020, 07:55 AM
it should still fix some issue You should use a java.nio.file.FileVisitor via java.nio.file.Files.walkFileTree(...). It has been introduced in Java 7 exactly for this use case.
Perl: reading all files of a directory, error: no such file or directory

Perl: reading all files of a directory, error: no such file or directory


By : Francis Cancio
Date : March 29 2020, 07:55 AM
it should still fix some issue You just need to prepend the directory to the elements of @files afterwards.
code :
foreach $file (@files) {
    open(my $fh, "$dir/$file") or die "Can't open $dir/$file: $!";
    while (<$fh>) { ... }
    # ...
}
Reading specific files in a directory in R

Reading specific files in a directory in R


By : user3305316
Date : March 29 2020, 07:55 AM
will help you I'm trying to list files in a directory , You could generate a regex pattern using your list of filenames:
code :
lst <- list("a", "b")
pat <- paste0("\\b(", paste(lst, collapse="|"), ")\\b")
files = list.files("folder/", pattern="csv")
files.keep <- grep(pat, files, value=TRUE)
files.keep

[1] "a.csv" "b.csv"
How to count number of files under specific directory in hadoop?

How to count number of files under specific directory in hadoop?


By : AmirAliZabihi
Date : March 29 2020, 07:55 AM
this will help The simplest/native approach is to use built in hdfs commands, in this case -count:
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