根据每组的数量添加列

Question

我想添加新闻栏目的每组在类型的计数。我的数据帧是这样的：

#   color  type  
#   black chair       
#   black chair   
#   black sofa 
#   pink  plate
#   pink  chair
#   red   sofa    
#   red   plate   

我正在寻找类似这样的东西：

#   color  chair sofa plate 
#   black    2     1   0
#   pink     1     0   1
#   red      0     1   1

我使用了table(df$color, df$type)，但是结果没有列'color‘的名称

Answer 1

我们可以使用来自base R的table

table(df)

或使用pivot_wider

library(tidyr)
pivot_wider(df, names_from = type, values_from = type, 
       values_fn = length, values_fill = 0)
# A tibble: 3 × 4
  color chair  sofa plate
  <chr> <int> <int> <int>
1 black     2     1     0
2 pink      1     0     1
3 red       0     1     1

或使用dcast

library(data.table)
dcast(setDT(df), color ~ type, value.var = 'type', length, fill = 0)

数据

df <- structure(list(color = c("black", "black", "black", "pink", "pink", 
"red", "red"), type = c("chair", "chair", "sofa", "plate", "chair", 
"sofa", "plate")), class = "data.frame", row.names = c(NA, -7L
))