Author

Sebastian Zeki

Published

July 23, 2018

Modified

March 23, 2024

There are many occasions when a column of data needs to be created from an already existing column for ease of data manipulation. For example, perhaps you have a body of text as a pathology report and you want to extract all the reports where the diagnosis is ‘dysplasia’.

You could just subset the data using grepl so that you only get the reports that mention this word…but what if the data needs to be cleaned prior to subsetting like excluding reports where the diagnosis is normal but the phrase ‘No evidence of dysplasia’ is present. Or perhaps there are other manipulations needed prior to subsetting.

This is where data accordionisation is useful. This simply means the creation of data from (usually) a column into another column in the same dataframe.

The neatest way to do this is with the mutate function from the {dplyr} package which is devoted to data cleaning. There are also other ways which I will demonstrate at the end.

The input data here will be an endoscopy data set:

Age <- sample(1:100, 130, replace = TRUE)
Dx <- sample(c("NDBE", "LGD", "HGD", "IMC"), 130, replace = TRUE)
TimeOfEndoscopy <- sample(1:60, 130, replace = TRUE)

library(dplyr)

EMRdf <- data.frame(Age, Dx, TimeOfEndoscopy, stringsAsFactors = F)

Perhaps you need to calculate the number of hours spent doing each endoscopy rather than the number of minutes

EMRdftbb <- EMRdf %>% mutate(TimeOfEndoscopy / 60)

# install.packages("knitr")
library(knitr)
library(kableExtra)

# Just show the top 20 results

kable(head(EMRdftbb, 20))
Age Dx TimeOfEndoscopy TimeOfEndoscopy/60
45 IMC 18 0.3000000
17 HGD 54 0.9000000
39 LGD 34 0.5666667
46 NDBE 55 0.9166667
31 NDBE 6 0.1000000
39 NDBE 4 0.0666667
21 IMC 17 0.2833333
29 HGD 44 0.7333333
78 IMC 18 0.3000000
56 NDBE 56 0.9333333
12 LGD 39 0.6500000
56 NDBE 2 0.0333333
56 LGD 60 1.0000000
4 HGD 28 0.4666667
68 LGD 56 0.9333333
73 NDBE 58 0.9666667
64 IMC 52 0.8666667
43 LGD 16 0.2666667
47 LGD 5 0.0833333
82 HGD 38 0.6333333

That is useful but what if you want to classify the amount of time spent doing each endoscopy as follows: <0.4 hours is too little time and >0.4 hours is too long.

Using ifelse() with mutate for conditional accordionisation.

For this we would use ifelse(). However this can be combined with mutate() so that the result gets put in another column as follows

EMRdf2 <- EMRdf %>%
  mutate(TimeInHours = TimeOfEndoscopy / 60) %>%
  mutate(TimeClassification = ifelse(TimeInHours > 0.4, "Too Long", "Too Short"))

# Just show the top 20 results

kable(head(EMRdf2, 20))
Age Dx TimeOfEndoscopy TimeInHours TimeClassification
45 IMC 18 0.3000000 Too Short
17 HGD 54 0.9000000 Too Long
39 LGD 34 0.5666667 Too Long
46 NDBE 55 0.9166667 Too Long
31 NDBE 6 0.1000000 Too Short
39 NDBE 4 0.0666667 Too Short
21 IMC 17 0.2833333 Too Short
29 HGD 44 0.7333333 Too Long
78 IMC 18 0.3000000 Too Short
56 NDBE 56 0.9333333 Too Long
12 LGD 39 0.6500000 Too Long
56 NDBE 2 0.0333333 Too Short
56 LGD 60 1.0000000 Too Long
4 HGD 28 0.4666667 Too Long
68 LGD 56 0.9333333 Too Long
73 NDBE 58 0.9666667 Too Long
64 IMC 52 0.8666667 Too Long
43 LGD 16 0.2666667 Too Short
47 LGD 5 0.0833333 Too Short
82 HGD 38 0.6333333 Too Long

Note how we can chain the mutate() function together.

Using multiple ifelse()

What if we want to get more complex and put several classifiers in? We just use more ifelse’s:

EMRdf2 <- EMRdf %>%
  mutate(TimeInHours = TimeOfEndoscopy / 60) %>%
  mutate(TimeClassification = ifelse(TimeInHours > 0.8, "Too Long", ifelse(TimeInHours < 0.5, "Too Short", ifelse(TimeInHours >= 0.5 & TimeInHours <= 0.8, "Just Right", "N"))))

# Just show the top 20 results

kable(head(EMRdf2, 20))
Age Dx TimeOfEndoscopy TimeInHours TimeClassification
45 IMC 18 0.3000000 Too Short
17 HGD 54 0.9000000 Too Long
39 LGD 34 0.5666667 Just Right
46 NDBE 55 0.9166667 Too Long
31 NDBE 6 0.1000000 Too Short
39 NDBE 4 0.0666667 Too Short
21 IMC 17 0.2833333 Too Short
29 HGD 44 0.7333333 Just Right
78 IMC 18 0.3000000 Too Short
56 NDBE 56 0.9333333 Too Long
12 LGD 39 0.6500000 Just Right
56 NDBE 2 0.0333333 Too Short
56 LGD 60 1.0000000 Too Long
4 HGD 28 0.4666667 Too Short
68 LGD 56 0.9333333 Too Long
73 NDBE 58 0.9666667 Too Long
64 IMC 52 0.8666667 Too Long
43 LGD 16 0.2666667 Too Short
47 LGD 5 0.0833333 Too Short
82 HGD 38 0.6333333 Just Right

Using multiple ifelse() with grepl() or string_extract

Of course we need to extract information from text as well as numeric data. We can do this using grepl() or string_extract() from the library(stringr).

Let’s say we want to extract all the samples that had IMC. We don’t want to subset the data, just extract IMC into a column that says IMC and the rest say ‘Non-IMC’

Using the dataset above:

library(stringr)

EMRdf$MyIMC_Column <- str_extract(EMRdf$Dx, "IMC")

# to fill the NAs we would do: EMRdf$MyIMC_Column <- ifelse(grepl("IMC",EMRdf$Dx),"IMC","NoIMC")

# Another way to do this (really should be for more complex examples when you want to extract the entire contents of the cell that has the match)

EMRdf$MyIMC_Column <- ifelse(grepl("IMC", EMRdf$Dx), str_extract(EMRdf$Dx, "IMC"), "NoIMC")

So data can be usefully created from data for further analysis.

Hopefully this way of extrapolating data and especially using conditional expressions to categorise data according to some rules is a helpful way to get more out of your data.

Please follow @gastroDS on twitter

This article originally appeared on https://sebastiz.github.io/gastrodatascience/ and has been edited to render in Quarto and had NHS-R styles applied.

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