常用基础知识

seq(from = 1, to = 1, by = ((to - from)/(length.out - 1)),
    length.out = NULL, along.with = NULL, ...)

举例----------Examples----------

seq(0, 1, length.out=11)
seq(stats::rnorm(20)) #  
seq(1, 9, by = 2)     #  
seq(1, 9, by = pi)    #  
seq(1, 6, by = 3)
seq(1.575, 5.125, by=0.05)
seq(17) # same as 1:17, or even better seq_len(17)

Loops

The most commonly used loop structures in R are for, while and apply loops. Less common are repeat loops. The break function is used to break out of loops, and next halts the processing of the current iteration and advances the looping index.

for(variable in sequence) { 
    statements
}
while(condition) statements
apply(X, MARGIN, FUN, ARGs)

保存为Tab分隔的txt文件：

write.table(y, file = paste("Day",a, " ",k, ".txt", sep=""), sep = "\t",row.names=FALSE)

data.frame 添加一行：
First, we create a one-row data frame with the new data:

newRow <- data.frame(city="West Dundee", county="Kane", state="IL", pop=5428)

Next, we use the rbind function to append that one-row data frame to our existing data frame:

suburbs <- rbind(suburbs, newRow)

data.frame 添加一列：

my.dataframe$new.col <- a.vector

my.dataframe[, "new.col"] <- a.vector

my.dataframe["new.col"] <- a.vector

df <- data.frame(b = runif(6), c = rnorm(6))
cbind(a = 0, df)

data <- read.table(header=TRUE, text='
id weight
  1     20
  2     27
  3     24
')

# Ways to add a column
data$size      <- c("small", "large", "medium")
data[["size"]] <- c("small", "large", "medium")
data[,"size"]  <- c("small", "large", "medium")
data$size      <- 0   # Use the same value (0) for all rows


# Ways to remove the column
data$size      <- NULL
data[["size"]] <- NULL
data[,"size"]  <- NULL
data[[3]]      <- NULL
data[,3]       <- NULL
data           <- subset(data, select=-size)

flush.console()

options(stringsAsFactors=FALSE)

A simple function to remove leading and trailing whitespace:

trim <- function( x ) {
  gsub("(^[[:space:]]+|[[:space:]]+$)", "", x)
}

Usage:

text = "   foo bar  baz 3 "
trim(text)
[1] "foo bar  baz 3"