转换混合单位测量

Question

我有一个包含大量非标准化英制和公制混合测量值的文件，我想对其进行标准化并重新发布。

该范围的示例如下所示：

df  <- data.frame(Measurements =c("1.25m", "2 Feet", "3 Inches", "5.5 cm"))

|Measurements|
|1.25m       |
|2 Feet      |
|3 Inches    |
|5.5 cm      |

我希望看起来像这样：

|Measurements|MM_Conversion|
|1.25m       |1200mm
|2 Feet      |609.6mm
|3 Inches    |76.2mm
|5.5 cm      |55mm

我不能使用measurements::conv_unit 或units::set_unit，因为它们似乎都需要数字输入值。有没有一种直接的方法可以同时解析值和字符串，并进行相应的转换？

编辑 1： 遇到 Conv_Unit 无法转换 NA 值的问题。如果初始向量改为：df <- data.frame(Measurements =c(NA, 1.25m", "2 Feet", "3 Inches", "5.5 cm"))，您将如何绕过它？

Answer 1

它可以（很容易）完成，但您必须先修复测量中的单位，因为接受来自 measurements::conv_unit 的长度单位

# accepted units
# $length
# [1] "angstrom" "nm"       "um"       "mm"       "cm"       "dm"       "m"        "km"       "inch"     "ft"       "yd"       "fathom"   "mi"       "naut_mi" 
# [15] "au"       "light_yr" "parsec"   "point" 

所以，英寸必须变成“英寸”，而“英尺”应该变成“英尺”（执行一些正则表达式魔术;-)）.. 但是......

library(tidyverse)
df  <- data.frame( Measurements =c( "1.25m", "2 ft", "3 inch", "5.5 cm" ) )

df %>% 
  #extract the numeric and the unit-parts from the string
  mutate( num_part = as.numeric( stringr::str_extract( Measurements, "\\d+\\.*\\d*" ) ), 
          unit_part = stringr::str_extract( Measurements, "[a-zA-Z]+" ) ) %>%
  #perform a rowwise operation
  rowwise() %>% 
  #convert the units to mm, row-by-row
  mutate( in_mm = conv_unit( num_part, unit_part, "mm" ) )

# Source: local data frame [4 x 4]
# Groups: <by row>
#   # A tibble: 4 x 4
#   Measurements num_part unit_part  in_mm
#   <fct>           <dbl> <chr>      <dbl>
# 1 1.25m            1.25 m         1250  
# 2 2 ft             2    ft         610. 
# 3 3 inch           3    inch        76.2
# 4 5.5 cm           5.5  cm          55  

Answer 2

我们可以使用 extract 和 tidyr 来分隔值和单位，然后使用 map2 将其输入到 conv_unit：

df <- data.frame(Measurements =c(NA, "1.25m", "2 Feet", "3 Inches", "5.5 cm"))

library(tidyverse)
library(stringr)
library(measurements)

df %>%
  extract(Measurements, c("value", "unit"), 
          regex = "^([\\d.]+)\\s*([[:alpha:]]+)$", 
          remove = FALSE, convert = TRUE) %>%
  mutate(unit = str_replace_all(unit, c(Feet="ft", Inches="inch")),
         MM_Conversion = paste0(map2(value, unit, ~if(!is.na(.x)) conv_unit(.x, .y, "mm") else NA), "mm"))

结果：

  Measurements value unit MM_Conversion
1         <NA>    NA <NA>          NAmm
2        1.25m  1.25    m        1250mm
3       2 Feet  2.00   ft       609.6mm
4     3 Inches  3.00 inch        76.2mm
5       5.5 cm  5.50   cm          55mm

如果NAs 不应出现在最终输出中，则使用filter：

df %>%
  extract(Measurements, c("value", "unit"), 
          regex = "^([\\d.]+)\\s*([[:alpha:]]+)$", 
          remove = FALSE, convert = TRUE) %>%
  filter(!is.na(Measurements)) %>%
  mutate(unit = str_replace_all(unit, c(Feet="ft", Inches="inch")),
         MM_Conversion = paste0(map2(value, unit, ~conv_unit(.x, .y, "mm")), "mm"))

结果：

  Measurements value unit MM_Conversion
1        1.25m  1.25    m        1250mm
2       2 Feet  2.00   ft       609.6mm
3     3 Inches  3.00 inch        76.2mm
4       5.5 cm  5.50   cm          55mm

请注意我如何手动缩写原始单位以使 conv_unit 工作。如果原始单位已经是缩写形式，那就少了一步。