rbindlist data.tables wtih列數不同

Question

我想知道我怎麼rbindlist不同數量的列數據表，並與來港填補空行像rbind.fill

DT1 = data.table(A=1:3) 
DT2 = data.table(A=4:5,B=letters[4:5]) 
l = list(DT1,DT2) 
rbindlist(l) 
    Error in rbindlist(l) : 
    Item 2 has 2 columns, inconsistent with item 1 which has 1 columns 

我要得到什麼是

A B 
1: 1 NA 
2: 2 NA 
3: 3 NA 
4: 4 d 
5: 5 e 

Answer 1

此功能現在在commit 1266 of v1.9.3中執行。從NEWS：

o 'rbindlist' gains 'use.names' and 'fill' arguments and is now implemented 
    entirely in C. Closes #5249  
    -> use.names by default is FALSE for backwards compatibility (doesn't bind by 
    names by default) 
    -> rbind(...) now just calls rbindlist() internally, except that 'use.names' 
    is TRUE by default, for compatibility with base (and backwards compatibility). 
    -> fill by default is FALSE. If fill is TRUE, use.names has to be TRUE. 
    -> At least one item of the input list has to have non-null column names. 
    -> Duplicate columns are bound in the order of occurrence, like base. 
    -> Attributes that might exist in individual items would be lost in the bound result. 
    -> Columns are coerced to the highest SEXPTYPE, if they are different, if/when possible. 
    -> And incredibly fast ;). 
    -> Documentation updated in much detail. Closes DR #5158. 

檢查this post爲基準。

---

實例：

1）使用的rbindlistfill論點：

DT1 <- data.table(x=1, y=2) 
DT2 <- data.table(y=2, z=-1) 

rbindlist(list(DT1, DT2), fill=TRUE) 
#  x y z 
# 1: 1 2 NA 
# 2: NA 2 -1 

注意，當fill=TRUE，use.names應TRUE。

---

2）具有重複名稱的適當綁定表：

DT1 <- data.table(x=1, x=2, y=1, y=2) 
DT2 <- data.table(y=3, y=-1, y=-2) 

rbindlist(list(DT1, DT2), fill=TRUE) 
#  x x y y y 
# 1: 1 2 1 2 NA 
# 2: NA NA 3 -1 -2 

---

3）它不僅限於data.tables，但它只是對data.frames和lists還有：

DT1 <- data.table(x=1, y=2) 
DT2 <- data.frame(y=2, z=-1) 
DT3 <- list(z=10) 

rbindlist(list(DT1,DT2,DT3), fill=TRUE) 

#  x y z 
# 1: 1 2 NA 
# 2: NA 2 -1 
# 3: NA NA 10 

---

4）如果你想用的名字只是綁定，可以設置只use.names=TRUE，但不fill：

DT1 <- data.table(x=1, y=2) 
DT2 <- data.table(y=1, x=2) 

rbindlist(list(DT1,DT2), use.names=TRUE, fill=FALSE) 
# x y 
# 1: 1 2 
# 2: 2 1 

DT1 <- data.table(x=1, y=2) 
DT2 <- data.table(z=2, y=1) 

# returns error when fill=FALSE but can't be bound without fill=TRUE 
rbindlist(list(DT1, DT2), use.names=TRUE, fill=FALSE) 
# Error in rbindlist(list(DT1, DT2), use.names = TRUE, fill = FALSE) : 
    # Answer requires 3 columns whereas one or more item(s) in the input 
    # list has only 2 columns. ... 

---

5）默認值是向後兼容（use.names=FALSE相同，fill=FALSE）：

DT1 <- data.table(x=1, y=2) 
DT2 <- data.table(y=1, x=2) 

rbindlist(list(DT1, DT2)) 

# x y 
# 1: 1 2 
# 2: 1 2 

HTH