mem_used.Rmd

# Rのコピー修正の例

## 元のデータを上書きしない場合

### `mutate()`

``` r
library(pryr)
library(dplyr, warn.conflicts = FALSE)
d <- tibble(x = 1:1000000, y = 1:1000000)
mem_change(x <- d %>% mutate(z = x * 2))
#> 8.18 MB
mem_used()
#> 59.5 MB
```

### `transmute()`

``` r
library(pryr)
library(dplyr, warn.conflicts = FALSE)
d <- tibble(x = 1:1000000, y = 1:1000000)
mem_change(x <- d %>% transmute(z = x * 2))
#> 8.28 MB
mem_used()
#> 59.6 MB
```


## 元のデータを上書きする場合

### `mutate()`

``` r
library(pryr)
library(dplyr, warn.conflicts = FALSE)
d <- tibble(x = 1:1000000, y = 1:1000000)
mem_change(d <- d %>% mutate(z = x * 2))
#> 8.18 MB
mem_used()
#> 59.5 MB
```

### `transmute()`

``` r
library(pryr)
library(dplyr, warn.conflicts = FALSE)
d <- tibble(x = 1:1000000, y = 1:1000000)
mem_change(d <- d %>% transmute(z = x * 2))
#> 276 kB
mem_used()
#> 51.6 MB
```