Creating a dataframe using declared variables

Question

I'm trying to create a dataframe to assist in downstream calculations. All "MineralVars" need an NA value in this 1-row dataframe. MineralVars will always change in length and variable names, so I can't create the dataframe by inputting each Mineral one at a time. I need to create it using the string 'MineralVars'.

# Declare variables
MineralVars <- c("Al", "Cu", "Pb")


# Create helper dataframe
Placeholder_df <- data.frame(make = "Placeholder", modelid = "Placeholder",
                             unitno = "Placeholder", compart = "Placeholder",
                             MineralVars = NA, meterread = NA, order = NA)

My desired dataframe would look like this;

Desired_df <- data.frame(sampledate = NA, make = "Placeholder", modelid = "Placeholder",
                            unitno = "Placeholder", compart = "Placeholder", oilchanged = "Placeholder",
                            Cu = NA, Pb = NA, Al = NA, meterread = NA, order = NA)

akrun · Accepted Answer · 2020-02-17 00:40:43Z

2

We can just do an assignment

Placeholder_df[MineralVars] <- NA

and remove the "MineralVars"

Placeholder_df["MineralVars"] <- NULL

Or use add_column

library(tibble)
library(dplyr)
add_column(Placeholder_df,.before = "MineralVars", 
    !!!setNames(rep(NA,length(MineralVars)), MineralVars))  %>%
      mutate(MineralVars = NULL)
 #      make     modelid      unitno     compart Al Cu Pb meterread order
#1 Placeholder Placeholder Placeholder Placeholder NA NA NA        NA    NA

and assign (<-) it either 'Placeholder_df' or a new object

edited Feb 17, 2020 at 0:40

answered Feb 17, 2020 at 0:35

akrun

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