英文:
Specify value after several conditions from different columns
问题
我正在努力寻找一种在数据框中选择特定行的正确方法，该方法基于来自不同列的多个条件，并尝试将给定值输入到该单元格中。我正在尝试找到一个基于dplyr的解决方案，但是经过几个小时的尝试后仍然找不到...
我创建了一个空列'C'，我想选择给定的'A'（因子）和该给定A的'B'（数值）的最大值（而不是整个B列的最大值），然后我想在相应的行的'C'列中写入'something'。
这是一个模拟我正在尝试做的事情的虚拟数据框：
A <- factor(c("19/09/2022", "19/09/2022", "19/09/2022", "20/09/2022", "20/09/2022", "20/09/2022", "21/09/2022", "21/09/2022", "21/09/2022", "22/09/2022", "22/09/2022", "22/09/2022"))B <- c(0.1781223, 3.3488114, 4.1476595, 5.8611553, 10.9773307, 16.9890155, 24.0428161, 35.1776457, 40.4551331, 49.5663783, 63.9132875, 64.6766946)df <- data.frame(A, B)
我创建了一个空列，我想要写入其中。
df$C <- NA
我尝试了类似于以下代码的方法，使用了case_when，但是出现了关于B的类型的错误：
df %>%filter(A == "19/09/2022") %>%mutate(C = case_when(B == max(B, na.rm = TRUE) ~ "something",B ~ NA))
谢谢你的帮助！
英文:
I am struggling to find the proper way to select a specific row in a dataframe, based on several conditions from different columns and to try to input a given value to that cell. I am trying to find a dplyr based solution, but can’t find any after several hours of trying…
I have created an empty column ‘C’, I want to select for a given ‘A’ (factor) and for the maximum value of ‘B’ (numeric) for that given A (not the max for the entire col B), then I want to write ‘something’ in the corresponding ‘C’ column for that row.
Here is a dummy DF replicating what I am trying to do:
A <- factor(c("19/09/2022", "19/09/2022", "19/09/2022", "20/09/2022", "20/09/2022", "20/09/2022", "21/09/2022", "21/09/2022", "21/09/2022", "22/09/2022", "22/09/2022", "22/09/2022"))B <- c(0.1781223, 3.3488114, 4.1476595, 5.8611553, 10.9773307, 16.9890155, 24.0428161, 35.1776457, 40.4551331, 49.5663783, 63.9132875, 64.6766946)df <- data.frame(A, B)
I create an empty column, in which I want to write.
df$C <- NA
I have tried something like this, using case_when, but there is an error on the type of B:
df %>%filter(A == "19/09/2022") %>%mutate(C = case_when(B == max(B, na.rm = T) ~ "something",B ~ NA))
Thank you for your help!
答案1
得分: 0
问题在于，在case_when中，LHS应该是一个逻辑向量，而在B ~ NA中，它是一个double（=B）。也许你想要的是case_when(B == max(B, na.rm = T) ~ "something", .default = NA)。
此外，由于你想要根据A的条件给C赋值，你需要使用group_by或mutate的.by参数对数据进行分组。另外，由于你只检查一个条件，你可以使用if_else：
library(dplyr)df %>%mutate(C = if_else(A == "19/09/2022" & B == max(B, na.rm = T),"something",NA),.by = A)#> A B C#> 1 19/09/2022 0.1781223 <NA>#> 2 19/09/2022 3.3488114 <NA>#> 3 19/09/2022 4.1476595 something#> 4 20/09/2022 5.8611553 <NA>#> 5 20/09/2022 10.9773307 <NA>#> 6 20/09/2022 16.9890155 <NA>#> 7 21/09/2022 24.0428161 <NA>#> 8 21/09/2022 35.1776457 <NA>#> 9 21/09/2022 40.4551331 <NA>#> 10 22/09/2022 49.5663783 <NA>#> 11 22/09/2022 63.9132875 <NA>#> 12 22/09/2022 64.6766946 <NA>
以上是给出的翻译结果，只包含代码部分的翻译。
英文:
The issue is that in case_when the LHS should be a logical vector whereas in B ~ NA it is a double (=B). Perhaps you want case_when(B == max(B, na.rm = T) ~ "something", .default = NA).
Moreover, as you want to assign a value to C based on a condition by A, you have to group your data using a group_by or the .by argument of mutate. Also, as you are only checking one condition you could go for an if_else:
library(dplyr)df %>%mutate(C = if_else(A == "19/09/2022" & B == max(B, na.rm = T),"something",NA),.by = A)#> A B C#> 1 19/09/2022 0.1781223 <NA>#> 2 19/09/2022 3.3488114 <NA>#> 3 19/09/2022 4.1476595 something#> 4 20/09/2022 5.8611553 <NA>#> 5 20/09/2022 10.9773307 <NA>#> 6 20/09/2022 16.9890155 <NA>#> 7 21/09/2022 24.0428161 <NA>#> 8 21/09/2022 35.1776457 <NA>#> 9 21/09/2022 40.4551331 <NA>#> 10 22/09/2022 49.5663783 <NA>#> 11 22/09/2022 63.9132875 <NA>#> 12 22/09/2022 64.6766946 <NA>
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