根据查找表替换数据框中的值 [英] Replace values in a dataframe based on lookup table

问题描述

我在替换数据框中的值时遇到了一些麻烦.我想替换基于单独表的值.以下是我要执行的操作的示例.

I am having some trouble replacing values in a dataframe. I would like to replace values based on a separate table. Below is an example of what I am trying to do.

我有一张桌子，每一行都是客户，每一列都是他们购买的动物.让我们将此数据帧称为table.

I have a table where every row is a customer and every column is an animal they purchased. Lets call this dataframe table.

> table
#       P1     P2     P3
# 1    cat lizard parrot
# 2 lizard parrot    cat
# 3 parrot    cat lizard

我还有一个要引用的表，称为lookUp.

I also have a table that I will reference called lookUp.

> lookUp
#      pet   class
# 1    cat  mammal
# 2 lizard reptile
# 3 parrot    bird

我想做的是创建一个名为new的新表，该表具有一个函数，将table中的所有值替换为lookUp中的class列.我自己使用lapply函数尝试了此操作，但收到以下警告.

What I want to do is create a new table called new with a function replaces all values in table with the class column in lookUp. I tried this myself using an lapply function, but I got the following warnings.

new <- as.data.frame(lapply(table, function(x) {
  gsub('.*', lookUp[match(x, lookUp$pet) ,2], x)}), stringsAsFactors = FALSE)

Warning messages:
1: In gsub(".*", lookUp[match(x, lookUp$pet), 2], x) :
  argument 'replacement' has length > 1 and only the first element will be used
2: In gsub(".*", lookUp[match(x, lookUp$pet), 2], x) :
  argument 'replacement' has length > 1 and only the first element will be used
3: In gsub(".*", lookUp[match(x, lookUp$pet), 2], x) :
  argument 'replacement' has length > 1 and only the first element will be used

关于如何进行这项工作的任何想法?

Any ideas on how to make this work?

推荐答案

您在问题中发布了一种不错的方法.这是一种更简单的方法:

You posted an approach in your question which was not bad. Here's a smiliar approach:

new <- df  # create a copy of df
# using lapply, loop over columns and match values to the look up table. store in "new".
new[] <- lapply(df, function(x) look$class[match(x, look$pet)])

一种更快的替代方法是:

An alternative approach which will be faster is:

new <- df
new[] <- look$class[match(unlist(df), look$pet)]

请注意，在两种情况下，我都使用空括号([])来保持new的结构(data.frame).

Note that I use empty brackets ([]) in both cases to keep the structure of new as it was (a data.frame).

(我在回答中使用的是df而不是table和look而不是lookup)

(I'm using df instead of table and look instead of lookup in my answer)

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