重塑數據表以使列名成為行名

Question

我在R有一個data.table

> dt
  SAMPLE   junction count
1: R1        a       1
2: R2        a       1
3: R3        b       1
4: R3        a       1
5: R1        c       2

現在我想“重塑”數據表以形成data frame m （基本上通過樣本矩陣連接，索引值為對應的計數值）。 另外，觀察到對於dt不存在的(SAMPLE,junction)對，我假設相應的count數值zero 。 有人可以幫助我如何實現這一目標嗎？

> m
      R1   R2   R3
  a    1    1    1
  b    0    0    1
  c    2    0    0

Answer 1

dcast的data.table將數據集從“long”格式更改為“wide”格式。

library(data.table)#v1.9.5+
dcast(dt, junction~SAMPLE, value.var='count', fill=0)
#   junction R1 R2 R3
#1:        a  1  1  1
#2:        b  0  0  1
#3:        c  2  0  0

如果需要矩陣輸出

library(reshape2)
acast(dt, junction~SAMPLE, value.var='count', fill=0)
#   R1 R2 R3
#a  1  1  1
#b  0  0  1
#c  2  0  0

或者來自base R xtabs

 xtabs(count~junction+SAMPLE, dt)

Answer 2

使用tidyr spread的另一種方法：

library(tidyr)

spread(dt, SAMPLE, count, fill=0)
#   junction R1 R2 R3
#1:        a  1  1  1
#2:        b  0  0  1
#3:        c  2  0  0

或與老同學的解決方案reshape從stats ：

reshape(dt, timevar='SAMPLE', idvar=c('junction'), direction='wide')
#   junction count.R1 count.R2 count.R3
#1:        a        1        1        1
#2:        b       NA       NA        1
#3:        c        2       NA       NA

數據：

dt = structure(list(SAMPLE = c("R1", "R2", "R3", "R3", "R1"), junction = c("a", 
"a", "b", "a", "c"), count = c(1, 1, 1, 1, 2)), .Names = c("SAMPLE", 
"junction", "count"), row.names = c(NA, -5L), class = c("data.table", 
"data.frame"), .internal.selfref = <pointer: 0x05e924a0>)