The Bigmemory Project

Xử lý dữ liệu có khả năng mở rộng trong R

Michael Kane

Assistant Professor, Yale University

bigmemory

bigmemory is used to store, manipulate, and process big matrices, that may be larger than a computer's RAM

big.matrix

Create
Retrieve
Subset
Summarize

What does "out-of-core" mean?

R objects are kept in RAM
When you run out of RAM
- Things get moved to disk
- Programs keep running (slowly) or crash

You are better off moving data to RAM only when the data are needed for processing.

When to use a big.matrix?

20% of the size of RAM
Dense matrices

An Overview of bigmemory

bigmemory implements the big.matrix data type, which is used to create, store, access, and manipulate matrices stored on the disk
Data are kept on the disk and moved to RAM implicitly

An Overview of bigmemory

A big.matrix object:

Only needs to be imported once
"backing" file
"descriptor" file

An example using bigmemory

library(bigmemory)

# Create a new big.matrix object
x <- big.matrix(nrow = 1, ncol = 3, type = "double", 
                init = 0, 
                backingfile = "hello_big_matrix.bin",
                descriptorfile = "hello_big_matrix.desc")

backing and descriptor files

backing file: binary representation of the matrix on the disk
descriptor file: holds metadata, such as number of rows, columns, names, etc..

An example using bigmemory

# See what's in it
 x[,]

  0    0    0

An object of class "big.matrix"
Slot "address":
<pointer: 0x108e2a9a0>

Similarities with matrices

# Change the value in the first row and column
x[1, 1] <- 3

# Verify the change has been made
x[,]

   3    0    0

Let's practice!

Xử lý dữ liệu có khả năng mở rộng trong R