How to test whether an uploaded Excel file meets requirements - r

Question

Background
Suppose I have a shiny app where the user can upload an Excel file. The users will have access to a certain Excel template and I want to make sure that only copies of this template are uploaded.
My current approach
My current approach is now as follows:
Check if sheet name xyz is present -> if not throw an error
Read data from sheet xyz, compare column names with requirements -> if missing columns throw an error
Repeat for all necessary sheets
Problem with the current approach
This requires a lot of hard coding required sheet names and required column names and becomes tedious.
Question
So my question: how can I assure that the user provides a valid file? What strategies do you usually use to make sure that the uploaded file can be properly processed by your apps?
Pseudo Code
library(shiny)
library(tidyverse)
ui <- fluidPage(fileInput("file", "Upload Excel"))
server <- function(input, output, session) {
observe({
req(input$file)
sheet1 <- tryCatch(read_xlsx(input$file$datapath, sheet = "xyz"),
error = function(e) {
## do some sort of error handling, e.g. write to a reactiveValue list
})
if (!all(.REQUIRED_FIELDS_FOR_XYZ %in% names(sheet1))) {
## signal error
}
})
}

Answer 1

If you are already using Excel, why not use a Macro to do the work for you. Consider listing file paths, checking format types, cell addresses, cell values, etc. The Macro below will do most of the heavy lifting for you.
Sub GetFolder_Data_Collection()
Dim colFiles As Collection, c As Range
Dim strPath As String, f, sht As Worksheet
Dim wbSrc As Workbook, wsSrc As Worksheet
Dim rw As Range
Dim sh As Worksheet, flg As Boolean
Set sht = ActiveSheet
strPath = ThisWorkbook.Path
Set colFiles = GetFileMatches(strPath, "*.xlsx", True)
With sht
.Range("A:I").ClearContents
.Range("A1").Resize(1, 5).Value = Array("Name", "Path", "Cell", "Value", "Numberformat")
Set rw = .Rows(2)
End With
For Each f In colFiles
Set wbSrc = Workbooks.Open(f)
Set wsSrc = wbSrc.Sheets(1)
For Each c In wsSrc.Range(wsSrc.Range("A1"), _
wsSrc.Cells(1, Columns.Count).End(xlToLeft)).Cells
rw.Cells(2).Value = wbSrc.Path
sht.Hyperlinks.Add Anchor:=rw.Cells(1), Address:=wbSrc.Path, TextToDisplay:=wbSrc.Name
rw.Cells(3).Value = c.Address(False, False)
rw.Cells(4).Value = c.Value
rw.Cells(5).Value = c.NumberFormat
i = 6
For Each sh In Worksheets
If sh.Name Like "Sheet1*" Or sh.Name Like "*Sheet2*" Then rw.Cells(i).Value = sh.Name & " Exists"
i = i + 1
Next
Set rw = rw.Offset(1, 0)
Next c
wbSrc.Close False
Next f
End Sub
'Return a collection of file objects given a starting folder and a file pattern
' e.g. "*.txt"
'Pass False for last parameter if don't want to check subfolders
Function GetFileMatches(startFolder As String, filePattern As String, _
Optional subFolders As Boolean = True) As Collection
Dim fso, fldr, f, subFldr
Dim colFiles As New Collection
Dim colSub As New Collection
Set fso = CreateObject("scripting.filesystemobject")
colSub.Add startFolder
Do While colSub.Count > 0
Set fldr = fso.GetFolder(colSub(1))
colSub.Remove 1
For Each f In fldr.Files
If UCase(f.Name) Like UCase(filePattern) Then colFiles.Add f
Next f
If subFolders Then
For Each subFldr In fldr.subFolders
colSub.Add subFldr.Path
Next subFldr
End If
Loop
Set GetFileMatches = colFiles
End Function
PUT THIS CODE IN AN XLSB OR XLSM EXCEL FILE IN THE SAME FOLDER AS YOUR EXCEL FILES.
It's probably just easier to do this kind of thing with Excel, and I'm a huge proponent of using the right tool for the job.