mutating a dataframe using values from another dataframe as variable names in R

Question

I want to loop through the rows in a r dataframe (df1) and create columns based on the variable values (v1) on each row. V1 is a column name on the dataframe df1. What I want to do is add a column using the name V1 onto df2. Variable v1 is of the data type <date> and the values will all be dates.

This is what I tried

  for(row in 1:nrow(df1)){
    df2 %>%
      mutate(row$v1 == "value")
  }

hotoku · Accepted Answer · 2020-04-12 03:25:30Z

1

Here's my answer

for(row in 1:nrow(df1)){
  colname <- df1[row, "v1"]
  df2[,colname] <- "value"
}

answered Apr 12, 2020 at 3:25

hotoku

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1 Comment

user8132864 Over a year ago

Thanks! Had to convert the colname into Character format since v1 was a date for(row in 1:nrow(df1)){ colname <- as.character(df1[row, "v1"]) df2[,colname] <- "value" } ```

Ronak Shah · Accepted Answer · 2020-04-12 10:56:29Z

0

You could do this directly without a loop :

df2[as.character(df1$v1)] <- 'value'

answered Apr 12, 2020 at 10:56

Ronak Shah

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Comments

akrun · Accepted Answer · 2020-04-12 14:56:28Z

0

We can also use

library(dplyr)
df2 %>%
   mutate_at(vars(as.character(df1$v1)), 'value')

answered Apr 12, 2020 at 14:56

akrun

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