r - data.frame更新时自动打印消息

Question

我希望 R 打印更新后的数据帧的尺寸，以显示我的每个步骤如何影响剩余的观察数量。通常，我的数据集大小会发生变化，因为存在 NA。我总是可以快速检查尺寸:

a = data.frame(a = c(1,2), b = c(3, NA))
na.omit(a) %>% dim

但我想在这一行中做两件事:

na.omit(a) %>% size
a <- na.omit(a)

因为代码因多次 dim() 调用而变得困惑。

有没有办法切换 R 的输出？类似的东西

a <- na.omit(a)
message: dimensions are now m x n

Answer 1

编辑:添加代码以仅在原始代码下对象发生更改时显示通知。

如果您只想在执行的每一行之后打印尺寸，您可以编写一个taskCallBack

tc <- addTaskCallback(function(...){message("Dimensions are: ", paste(dim(a), collapse = " "));return(TRUE)})

# When you want to remove the callback
removeTaskCallback(tc)

这是一个正在使用的示例 session 。您可能可以修改taskCallBack，使其仅在情况发生变化时才打印。

> a <- mtcars
> 
> tc <- addTaskCallback(function(...){message("Dimensions are: ", paste(dim(a), collapse = " "));return(TRUE)})
Dimensions are: 32 11
> 
> a
                     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
Hornet 4 Drive      21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
Hornet Sportabout   18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
Valiant             18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
Duster 360          14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
Merc 240D           24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
Merc 230            22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
Merc 280            19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4
Merc 280C           17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
Merc 450SE          16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3
Merc 450SL          17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3
Merc 450SLC         15.2   8 275.8 180 3.07 3.780 18.00  0  0    3    3
Cadillac Fleetwood  10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4
Lincoln Continental 10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4
Chrysler Imperial   14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4
Fiat 128            32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
Honda Civic         30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
Toyota Corolla      33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
Toyota Corona       21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
Dodge Challenger    15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2
AMC Javelin         15.2   8 304.0 150 3.15 3.435 17.30  0  0    3    2
Camaro Z28          13.3   8 350.0 245 3.73 3.840 15.41  0  0    3    4
Pontiac Firebird    19.2   8 400.0 175 3.08 3.845 17.05  0  0    3    2
Fiat X1-9           27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
Porsche 914-2       26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
Lotus Europa        30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
Ford Pantera L      15.8   8 351.0 264 4.22 3.170 14.50  0  1    5    4
Ferrari Dino        19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6
Maserati Bora       15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8
Volvo 142E          21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2
Dimensions are: 32 11
> a <- a[1:5,]
Dimensions are: 5 11
> 
> # When you want to remove the callback
> removeTaskCallback(tc)
[1] TRUE

如果您只想在对象更改时接收通知，我们可以编写更多内容来实际监视对象并仅在适当时显示消息。这是我将使用的代码:

# @object_name - Character string. The object name you want to montior
# @example tc <- addTaskCallback(monitor_object("mtcars"))
monitor_object <- function(object_name){
    object_dim <- NULL
    if(exists(object_name)){
        object_dim <- dim(get(object_name))
    }

    f <- function(...){
        new_dim <- NULL
        if(exists(object_name)){
            new_dim <- dim(get(object_name))
        }
        if(!identical(new_dim, object_dim)){


            msg <- paste0(object_name, 
                         " changed.\nOld dimensions: ", 
                         paste(object_dim, collapse = " "),
                         "\nNew dimensions: ",
                         paste(new_dim, collapse = " "))
            object_dim <<- new_dim
            message(msg)
        }
        return(TRUE)
    }

    return(f)
}

tc <- addTaskCallback(monitor_object("mtcars"))

# When you want to remove the callback
removeTaskCallback(tc)

还有一个示例 session ...

> tc <- addTaskCallback(monitor_object("mtcars"))
> mtcars <- mtcars[,-1]
mtcars changed.
Old dimensions: 32 11
New dimensions: 32 10
> head(mtcars)
                  cyl disp  hp drat    wt  qsec vs am gear carb
Mazda RX4           6  160 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag       6  160 110 3.90 2.875 17.02  0  1    4    4
Datsun 710          4  108  93 3.85 2.320 18.61  1  1    4    1
Hornet 4 Drive      6  258 110 3.08 3.215 19.44  1  0    3    1
Hornet Sportabout   8  360 175 3.15 3.440 17.02  0  0    3    2
Valiant             6  225 105 2.76 3.460 20.22  1  0    3    1
> mtcars <- mtcars[1:5,]
mtcars changed.
Old dimensions: 32 10
New dimensions: 5 10

我实际上扩展了这段代码，因为这是一个有趣的小练习，并且使您可以指定要用于监视对象的函数。我做了一个gist for the function that can be found here.