R语言二进制文件|极客教程

R语言二进制文件

二进制文件是一种只以位和字节（0和1）形式存储信息的文件。它们无法被人类阅读，因为其中的字节会转换成包含许多其他不可打印字符的字符和符号。使用任何文本编辑器尝试读取二进制文件将显示像Ø和ð这样的字符。

二进制文件必须由特定的程序来读取以便使用。例如，Microsoft Word程序的二进制文件只能通过Word程序转换成可读的形式。这表明，除了可读的文本之外，还有许多其他信息，如字符格式和页码等，也与字母数字字符一起存储。最后，二进制文件是一个连续的字节序列。我们在文本文件中看到的换行符是一个字符将第一行与下一行连接起来。

有时，R需要以二进制文件的形式处理其他程序生成的数据。同时，R还需要创建可以与其他程序共享的二进制文件。

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

语法

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

以下是参数的描述：

con 是用于读取或写入二进制文件的连接对象。
object 是要写入的二进制文件。
what 是表示要读取的字节的模式，如字符、整数等。
n 是从二进制文件中读取的字节数。

示例

我们将考虑R内置的数据集”mtcars”。首先，我们将其保存为CSV文件，然后将其转换为二进制文件并保存为操作系统文件。接下来，我们将读取创建的这个二进制文件。

写入二进制文件

我们将数据框”mtcars”作为CSV文件读入，然后将其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.mtcarscyl,new.mtcarsam,new.mtcars$gear), write.filename)

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

读取二进制文件

上面创建的二进制文件将所有数据存储为连续的字节。因此，我们将通过选择适当的列名和列值来读取它。

# 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)

当我们执行上面的代码时，它会产生以下的结果和图表 −

[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