R 简明教程

R - Binary Files

二进制文件是一个仅以位和字节(0 和 1)形式存储信息的 file。它们不可读,因为其中的字节转换为包含许多其他不可打印字符的字符和符号。尝试使用任何文本编辑器读取二进制文件将显示类似于 Ø 和 ð 的字符。

二进制文件必须由特定程序读取才能使用。例如,Microsoft Word 程序的二进制文件只能由 Word 程序读取为人类可读的形式。这表明,除了人类可读文本之外,还有更多信息,例如字符格式和页码等,这些信息也与字母数字字符一起存储。最后,二进制文件是连续的字节序列。我们在文本文件中看到的换行符是连接第一行和下一行的字符。

有时,需要由 R 将其他程序生成的数据作为二进制文件处理。还需要 R 创建可以与其他程序共享的二进制文件。

R 有两个函数 WriteBin()readBin() 来创建和读取二进制文件。

Syntax

writeBin(object, con)
readBin(con, what, n )

以下是所用参数的描述 -

  1. con 是读取或写入二进制文件的连接对象。

  2. object 是要写入的二进制文件。

  3. what 是表示要读取的字节的模式,例如字符、整数等。

  4. n 是要从二进制文件读取的字节数。

Example

我们考虑 R 内置数据“mtcars”。首先,我们从中创建一个 csv 文件,并将其转换为二进制文件并将其存储为 OS 文件。接下来,我们将创建的此二进制文件读入 R。

Writing the Binary File

我们将数据框“mtcars”读作 csv 文件,然后作为二进制文件写入操作系统。

# Read the "mtcars" data frame as a csv file and store only the columns
   "cyl", "am" and "gear".
write.table(mtcars, file = "mtcars.csv",row.names = FALSE, na = "",
   col.names = TRUE, sep = ",")

# Store 5 records from the csv file as a new data frame.
new.mtcars <- read.table("mtcars.csv",sep = ",",header = TRUE,nrows = 5)

# Create a connection object to write the binary file using mode "wb".
write.filename = file("/web/com/binmtcars.dat", "wb")

# Write the column names of the data frame to the connection object.
writeBin(colnames(new.mtcars), write.filename)

# Write the records in each of the column to the file.
writeBin(c(new.mtcars$cyl,new.mtcars$am,new.mtcars$gear), write.filename)

# Close the file for writing so that it can be read by other program.
close(write.filename)

Reading the Binary File

上面创建的二进制文件将所有数据存储为连续字节。因此,我们将通过选择列名以及列值来读取它。

# Create a connection object to read the file in binary mode using "rb".
read.filename <- file("/web/com/binmtcars.dat", "rb")

# First read the column names. n = 3 as we have 3 columns.
column.names <- readBin(read.filename, character(),  n = 3)

# Next read the column values. n = 18 as we have 3 column names and 15 values.
read.filename <- file("/web/com/binmtcars.dat", "rb")
bindata <- readBin(read.filename, integer(),  n = 18)

# Print the data.
print(bindata)

# Read the values from 4th byte to 8th byte which represents "cyl".
cyldata = bindata[4:8]
print(cyldata)

# Read the values form 9th byte to 13th byte which represents "am".
amdata = bindata[9:13]
print(amdata)

# Read the values form 9th byte to 13th byte which represents "gear".
geardata = bindata[14:18]
print(geardata)

# Combine all the read values to a dat frame.
finaldata = cbind(cyldata, amdata, geardata)
colnames(finaldata) = column.names
print(finaldata)

当我们执行上述代码时,它会产生以下结果和图表:

 [1]    7108963 1728081249    7496037          6          6          4
 [7]          6          8          1          1          1          0
[13]          0          4          4          4          3          3

[1] 6 6 4 6 8

[1] 1 1 1 0 0

[1] 4 4 4 3 3

     cyl am gear
[1,]   6  1    4
[2,]   6  1    4
[3,]   4  1    4
[4,]   6  0    3
[5,]   8  0    3

正如我们所看到的,我们通过在 R 中读取二进制文件获取了原始数据。