中間生成なしでカラム名を変更する５つの方法
中間生成なしでカラム名を変更する
中間生成的なことをせずに、dataframeのカラム名を変更するには、
dplyr::rename、magrittr::set_names、data.table::setnames
の３つがある (知っている限り
data_frame(a = 1:5, b = 2:6) %>%
dplyr::rename(a2 = a, b2 = b)
## Source: local data frame [5 x 2]
##
## a2 b2
## (int) (int)
## 1 1 2
## 2 2 3
## 3 3 4
## 4 4 5
## 5 5 6
data_frame(a = 1:5, b = 2:6) %>%
magrittr::set_names(x = ., value = c("a2", "b2"))
## Source: local data frame [5 x 2]
##
## a2 b2
## (int) (int)
## 1 1 2
## 2 2 3
## 3 3 4
## 4 4 5
## 5 5 6
data_frame(a = 1:5, b = 2:6) %>%
data.table::setnames(c("a2", "b2")) %>%
print
## Source: local data frame [5 x 2]
##
## a2 b2
## (int) (int)
## 1 1 2
## 2 2 3
## 3 3 4
## 4 4 5
## 5 5 6
と思っていたけど、dplyr::selectでもいける。
data_frame(a = 1:5, b = 2:6) %>%
select(a2 = a, b2 = b)
## Source: local data frame [5 x 2]
##
## a2 b2
## (int) (int)
## 1 1 2
## 2 2 3
## 3 3 4
## 4 4 5
## 5 5 6
# 他のカラムも残す
data_frame(a = 1:5, b = 2:6, c = 3:7, d = 4:8) %>%
select(a2 = a, everything())
## Source: local data frame [5 x 4]
##
## a2 b c d
## (int) (int) (int) (int)
## 1 1 2 3 4
## 2 2 3 4 5
## 3 3 4 5 6
## 4 4 5 6 7
## 5 5 6 7 8
「selectで列の複製ができるのでは？」と思って、以下のようなコードを書いた結果だめだったので気づいた
# やったこと
data_frame(a = 1:5, b = 2:6) %>%
select(a2 = a, a3 = a, b2 = b)
## Source: local data frame [5 x 2]
##
## a3 b2
## (int) (int)
## 1 1 2
## 2 2 3
## 3 3 4
## 4 4 5
## 5 5 6
# ほしかったもの
data_frame(a = 1:5, b = 2:6) %>%
mutate(a2 = a, a3 = a, b2 = b) %>%
select(-a, -b)
## Source: local data frame [5 x 3]
##
## a2 a3 b2
## (int) (int) (int)
## 1 1 1 2
## 2 2 2 3
## 3 3 3 4
## 4 4 4 5
## 5 5 5 6
dplyr::tranmuteで１行にまとめる
# もう少しよい道筋
data_frame(a = 1:5, b = 2:6) %>%
transmute(a2 = a, a3 = a, b2 = b)
## Source: local data frame [5 x 3]
##
## a2 a3 b2
## (int) (int) (int)
## 1 1 1 2
## 2 2 2 3
## 3 3 3 4
## 4 4 4 5
## 5 5 5 6
とりあえず、速さくらべ
colnames_rename <-
function(iter){
for(i in 1:iter){
data_frame(a = 1:5, b = 2:6) %>%
dplyr::rename(a2 = a, b2 = b)
}
}
colnames_set_names <-
function(iter){
for(i in 1:iter){
data_frame(a = 1:5, b = 2:6) %>%
magrittr::set_names(x = ., value = c("a2", "b2"))
}
}
colnames_setnames <-
function(iter){
for(i in 1:iter){
data_frame(a = 1:5, b = 2:6) %>%
data.table::setnames(c("a2", "b2"))
}
}
colnames_select <-
function(iter){
for(i in 1:iter){
data_frame(a = 1:5, b = 2:6) %>%
dplyr::select(a2 = a, b2 = b)
}
}
colnames_transmute <-
function(iter){
for(i in 1:iter){
data_frame(a = 1:5, b = 2:6) %>%
dplyr::transmute(a2 = a, b2 = b)
}
}
(time_dplyr_rename <- system.time(colnames_rename(10000)))
## user system elapsed
## 4.047 0.024 4.091
(time_mag <- system.time(colnames_set_names(10000)))
## user system elapsed
## 2.171 0.009 2.199
(time_dt <- system.time(colnames_setnames(10000)))
## user system elapsed
## 2.434 0.008 2.452
(time_dplyr_select <- system.time(colnames_select(10000)))
## user system elapsed
## 4.324 0.017 4.375
(time_dplyr_transmute <- system.time(colnames_transmute(10000)))
## user system elapsed
## 10.245 0.092 11.241
# とりあえず可視化する
data_frame(funs = factor(c("dplyr::rename", "dplyr::select", "dplyr::transmute", "magrittr::set_names", "data.table::setnames")),
Time = c(time_dplyr_rename[3], time_dplyr_select[3], time_dplyr_transmute[3], time_mag[3], time_dt[3])) %>%
ggplot(aes(x = funs, y = Time, fill = funs)) +
geom_bar(stat = "identity") +
guides(fill = F)
transmuteがかなり遅く、set_names、setnamesが速い
とはいえ
- カラム名変更を繰り返すシチュエーションが考えづらいこと
- 列名が多いデータ (wide形式) をほとんど使わないこと
から無視してもよさそう
それと、データハンドリングの過程でmutate, selectに頼らないパターンが稀なので、
その意味でもdplyr系をわざわざ外すメリットが少ない気がする。
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## date 2016-04-01
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