r/man/ParquetFileReader.Rd

% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/parquet.R
\docType{class}
\name{ParquetFileReader}
\alias{ParquetFileReader}
\title{ParquetFileReader class}
\description{
This class enables you to interact with Parquet files.
}
\section{Factory}{


The \code{ParquetFileReader$create()} factory method instantiates the object and
takes the following arguments:
\itemize{
\item \code{file} A character file name, raw vector, or Arrow file connection object
(e.g. \code{RandomAccessFile}).
\item \code{props} Optional \link{ParquetArrowReaderProperties}
\item \code{mmap} Logical: whether to memory-map the file (default \code{TRUE})
\item \code{...} Additional arguments, currently ignored
}
}

\section{Methods}{

\itemize{
\item \verb{$ReadTable(column_indices)}: get an \code{arrow::Table} from the file. The optional
\verb{column_indices=} argument is a 0-based integer vector indicating which columns to retain.
\item \verb{$ReadRowGroup(i, column_indices)}: get an \code{arrow::Table} by reading the \code{i}th row group (0-based).
The optional \verb{column_indices=} argument is a 0-based integer vector indicating which columns to retain.
\item \verb{$ReadRowGroups(row_groups, column_indices)}: get an \code{arrow::Table} by reading several row groups (0-based integers).
The optional \verb{column_indices=} argument is a 0-based integer vector indicating which columns to retain.
\item \verb{$GetSchema()}: get the \code{arrow::Schema} of the data in the file
\item \verb{$ReadColumn(i)}: read the \code{i}th column (0-based) as a \link{ChunkedArray}.
}
}

\section{Active bindings}{

\itemize{
\item \verb{$num_rows}: number of rows.
\item \verb{$num_columns}: number of columns.
\item \verb{$num_row_groups}: number of row groups.
}
}

\examples{
\dontrun{
f <- system.file("v0.7.1.parquet", package="arrow")
pq <- ParquetFileReader$create(f)
pq$GetSchema()
if (codec_is_available("snappy")) {
  # This file has compressed data columns
  tab <- pq$ReadTable()
  tab$schema
}
}
}