在单个条件下使用data.table替换多列 [英] using data.table to replace multiple columns on single condition

问题描述

我想将默认值(255)更改为NA.

I want to change the default value (which is 255) to NA.

dt <- data.table(x = c(1,5,255,0,NA), y = c(1,7,255,0,0), z = c(4,2,7,8,255))
coords <- c('x', 'y')

其中提供以下代码:

     x   y   z
1:   1   1   4
2:   5   7   2
3: 255 255   7
4:   0   0   8
5:  NA   0 255

我想出的最远的是这个:

I the furthest I came up with is this:

dt[.SD == 255, (.SD) := NA, .SDcols = coords]

请注意，z列保持不变.因此，仅指定的列而不是所有的列.

Please note that column z stays the same. So just the columns which are specified and not all columns.

但这并不能帮助我获得解决方案:

But that doesn't help me to get the sollution:

     x   y   z
1:   1   1   4
2:   5   7   2
3:  NA  NA   7
4:   0   0   8
5:  NA   0 255

我正在寻找一种可持续的解决方案，因为原始数据集有几百万行.

I am looking for a sustainable solution because the original dataset is a couple of million rows.

我找到了一个解决方案，但是它相当丑陋，而且肯定太慢了，因为它要花费近10秒钟才能通过22009 x 86的数据帧.有人能找到更好的解决方案吗?

I have found a solution but it is quite ugly and is definately too slow as it takes almost 10 seconds to get through a dataframe of 22009 x 86. Does anyone have a better solution?

代码:

dt [，replace(.SD，.SD == 255，NA)，.SDcols =坐标，by = c(colnames(dt)[！colnames(dt)％in％coords])]

推荐答案

在这里，您可以将列保留在 .SDcols ，

Here is how you can keep the columns outside .SDcols,

library(data.table)
dt[, (coords) := replace(.SD, .SD == 255, NA), .SDcols = coords]

给出，

    x  y   z
1:  1  1   4
2:  5  7   2
3: NA NA   7
4:  0  0   8
5: NA  0 255

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