1、melt: 短数据转长数据

（1）、融合的数据为数组、表以及矩阵，melt的表达式为：

melt(data, varnames = names(dimnames(data)), ..., na.rm = FALSE, as.is = FALSE, value.name = "value")长

na.rm表示缺失值处理办法，value.name用于重命名值所在列的名称

melt(data, id.vars, measure.vars, variable.name = "variable", ..., na.rm = FALSE, value.name = "value", factorsAsStrings = TRUE)

id.vars ：设置融合后单独显示的变量，可以用变量位置及名称表示,没写表示使用所有非measure.vars值

measure.vars ：通常根据id.vars 设置的变化而变化，也可以用变量位置及名称表示

variable.name ：name of variable used to store measured variable names

value.name ：name of variable used to store values

melt(data, ..., level = 1)/

x<-data.frame(id=1:6,

name=c("wang","zhang","li","chen","zhao","song"),

shuxue=c(89,85,68,79,96,53),

yuwen=c(77,68,86,87,92,63))

melt(x,id.vars=c("id","name")) #id参数表示第1，2列不变

melt(x,id.vars=1:2,variable.name="kemu",value.name="zhi")

melt(x,measure.vars=c("id","name"))