CODEWITHSUNDEEP
rdataframedplyraggregate
Enrique Dominguez
Enrique Dominguez

Reputation: 21

How to use two column values of a dataframe to select a value from another dataframe in R?

I hope you are doing well.

This is the dataset I'm using

Data set

I want to calculate the change of the BMI of the users of the App. I got the Id's, the first date of record and the last with the following code

BMI_results <- weight_log %>% 
    group_by(Id) %>% 
    summarize(date_min = min(Date), date_max = max(Date)) 

BMI_results

The next part is to use that data to get the corresponding BMI of that dates and then substract those numbers. This is the part where I'm stuck. Please help.

# The following code is wrong, just for illustration:

BMI_results <- weight_log %>% 
    group_by(Id) %>% 
    summarize(date_min = min(Date), date_max = max(Date)) %>%
    mutate(
            first_BMI = filter(weight_log$BMI, 
                               Id == Id & date_min == Date), 
            last_BMI = filter(weight_log$BMI, 
                              Id == Id & date_max == Date),
            difference = first_BMI-last_BMI 
          )

I was expecting to get the values of each BMI, the first and last recorded, and then substract them.

Upvotes: 1

Views: 34

Answers (1)

MrFlick
MrFlick

Reputation: 206187

Try something like

BMI_results <- weight_log %>% 
    group_by(Id) %>% 
    arrange(Date) %>%
    summarize(diff=first(BMI)-last(BMI))

Upvotes: 0

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