R语言学习笔记-reshape2

reshape2是一个强大的数据处理操作的R包。
主要函数，melt,*cast.两个函数

melt

###S3 method for class 'data.frame'melt(data, id.vars, measure.vars,  variable.name = "variable", ..., na.rm = FALSE, value.name = "value",factorsAsStrings = TRUE)### Default（vector） S3 method: melt(data, ..., na.rm = FALSE, value.name = "value")### S3 method for class 'list' melt(data, ..., level = 1)### S3 method for class 'array''table''matrix' melt(data, varnames = names(dimnames(data)), ...,  na.rm = FALSE, as.is = FALSE, value.name = "value")

melt_example

###data.frame###head(airquality)ozone solar.r wind temp month day  41     190  7.4   67     5   1  36     118  8.0   72     5   2  12     149 12.6   74     5   3  18     313 11.5   62     5   4  NA      NA 14.3   56     5   5melt(airquality, id=c("month", "day")) month day variable value   5   1    ozone    41   5   2    ozone    36   5   3    ozone    12   5   4    ozone    18 ###matrix,array,list### a <- array(c(1:8,NA), c(3,3)) a      [,1] [,2] [,3][1,]    1    4    7[2,]    2    5    8[3,]    3    6   NAmelt(a)   Var1 Var2 value1    1    1     12    2    1     23    3    1     34    1    2     45    2    2     5#Var1,Var2为value的下标，三维同上(增加Var3),list增加l1列，表列表位置

*cast

acast,dcast的区别在于输出结果。 acast 输出结果为vector/matrix/array, dcast 输出结果为data.frame.参数formula中，.表示后面没有数据列，…表示之前或之后的所有数据列

*cast(data, formula, fun.aggregate = NULL, ..., margins = NULL,  subset = NULL, fill = NULL, drop = TRUE,  value.var = guess_value(data))##Arguments解释##formula指的是处理公式。fun.aggregate为计算公式。subset 为帅选规则,plyr包可扩展其功能.

*cast_example

aqm <- melt(airquality, id=c("month", "day"), na.rm=TRUE)head(aqm)    month day variable value1     5   1    ozone    412     5   2    ozone    363     5   3    ozone    124     5   4    ozone    18acast(aqm, day ~ month ~ variable) ##按照month,day,variable,分割数据,返还数组., , ozone     5  6   7   8  91   41 NA 135  39 962   36 NA  49   9 78 , , solar.r     5   6   7   8   91  190 286 269  83 1672  118 287 248  24 197, , wind      5    6    7    8    91   7.4  8.6  4.1  6.9  6.92   8.0  9.7  9.2 13.8  5.1, , temp    5  6  7  8  91  67 78 84 81 912  72 74 85 81 92##结果中X为day,Y为Month,Z为variable##acast(aqm, formula=month ~ variable, fun.aggregate=mean)#按month,variable切割,并求均值     ozone  solar.r      wind     temp5 23.61538 181.2963 11.622581 65.548396 29.44444 190.1667 10.266667 79.10000······##行名为month,列名为variable,结果类型为矩阵dcast(aqm, month ~ variable, mean, margins = TRUE)    month    ozone   solar.r    wind     temp      (all)1     5    23.61538  181.2963 11.622581 65.54839  68.706962     6    29.44444  190.1667 10.266667 79.10000  87.38384······6  （all)  42.12931  185.9315  9.957516  77.88235  80.05722##行名为month,列名为variable,结果类型为数据框，margins对整体进行处理。library(plyr)acast(aqm, variable ~ month, mean, subset = .(variable == "ozone"))  5        6        7        8        9ozone 23.61538 29.44444 59.11538 59.96154 31.44828

其他函数

colsplit(string, pattern, names)##examle###x[1] "a_1" "a_2" "b_2" "c_3"vars <- colsplit(x, "_", c("trt", "time"))   trt time1   a    12   a    23   b    24   c    3