reshape包常用函数操作

melt 宽边长； dcast 长边宽

library(reshape2)
x <- data.frame(k1 = c(NA, NA, 3, 4, 5), k2 = c(1, NA, NA, 
    4, 5), data = 1:5)
y <- data.frame(k1 = c(NA, 2, NA, 4, 5), k2 = c(NA, NA, 3, 
    4, 5), data = 1:5)
res1 <- merge(x, y, by = "k1")
knitr::kable(head(res1))

k1	k2.x	data.x	k2.y	data.y
4	4	4	4	4
5	5	5	5	5
NA	1	1	NA	1
NA	1	1	3	3
NA	NA	2	NA	1
NA	NA	2	3	3

res2 <- merge(x, y, by = c("k1", "k2"))
knitr::kable(head(res2))

k1	k2	data.x	data.y
4	4	4	4
5	5	5	5
NA	NA	2	1

names(airquality) <- tolower(names(airquality))
knitr::kable(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	5
28	NA	14.9	66	5	6

aql <- melt(airquality)

## No id variables; using all as measure variables

knitr::kable(head(aql))

variable	value
ozone	41
ozone	36
ozone	12
ozone	18
ozone	NA
ozone	28

aql <- melt(airquality, id.vars = c("month", "day"))
knitr::kable(head(aql))

month	day	variable	value
5	1	ozone	41
5	2	ozone	36
5	3	ozone	12
5	4	ozone	18
5	5	ozone	NA
5	6	ozone	28

aqw <- dcast(aql, month + day ~ variable)
knitr::kable(head(aqw))

month	day	ozone	solar.r	wind	temp
5	1	41	190	7.4	67
5	2	36	118	8.0	72
5	3	12	149	12.6	74
5	4	18	313	11.5	62
5	5	NA	NA	14.3	56
5	6	28	NA	14.9	66

knitr::kable(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	5
28	NA	14.9	66	5	6

d1 <- dcast(aql, month ~ variable)

## Aggregation function missing: defaulting to length

knitr::kable(d1)

month	ozone	solar.r	wind	temp
5	31	31	31	31
6	30	30	30	30
7	31	31	31	31
8	31	31	31	31
9	30	30	30	30

d2 <- dcast(aql, month ~ variable, fun.aggregate = mean, na.rm = TRUE)
knitr::kable(d2)

month	ozone	solar.r	wind	temp
5	23.61538	181.2963	11.622581	65.54839
6	29.44444	190.1667	10.266667	79.10000
7	59.11538	216.4839	8.941935	83.90323
8	59.96154	171.8571	8.793548	83.96774
9	31.44828	167.4333	10.180000	76.90000