Comparing column headers of two files to fetch data in R - r

Question

I have a large CSV file, say INPUT, with about 500+ columns. I also have a dataframe DF that contains a subset of the column headers of INPUT which changes at every iteration.
I have to fetch the data from only those columns of INPUT that is present in the dataframe DF and write it into another CSV file, say OUTPUT.
In short,
INPUT.csv:
ID,Col_A,Col_B,Col_C,Col_D,Col_E,Col_F,,,,,,,,,,,,,Col_S,,,,,,,,,,,,,,,,Col_Z
1,009,abcd,67,xvz,33,50,,,,,,,,,,,,,,,,,,,,,,,,,,,,oup,,,,,,,,,,,,,,,,,,90
2,007,efgh,87,wuy,56,67,,,,,,,,,,,,,,,,,,,,,,,,,,,,ghj,,,,,,,,,,,,,,,,,,,,888
print(DF):
[1] "Col_D" "Col_Z"
[3] "Col_F" "Col_S"
OUTPUT.csv
ID,Col_D,Col_Z,Col_F,Col_S
1,xvz,90,50,oup
2,wuy,888,67,ghj
I'm a beginner when it comes to R. I would prefer for the matching of dataframe with the INPUT file to be automated, because i don't want to do this everyday when the dataframe gets updated.

Answer 1

I'm not sure whether this is the answer :
input <- read.table(...)
input[colnames(input) %in% colnames(DF)]

Answer 2

if I understand it correctly, you need to import the INPUT.csv file inside R and then match the columns of your DF with those columns of your INPUT, is that correct?
you can either use the match function or just import the INPUT.csv file inside RStudio via "Import Dataset" button and subset it. Subsetting of imported dataframes is fairly easy.
If you will import your dataset as INPUT, then you can make the subset of these columns in following way: INPUT[,c(1,2,4)]
and that will get you first, second and fourth column of the INPUT dataset.

Answer 3

First, to upload the csv is simple:
dataframe_read <- read.csv('/Path/to/csv/')
If I understand correctly that one dataframes columns is always a subset, the code is as follows:
### Example Dataframes
df1 <- data_frame(one = c(1,3,4), two= c(1,2,3), three = c(1,2,3))
df2 <- data_frame(one = c(1,3,4), three= c(1,2,3))
### Make new data frame
df3 <- df1[,colnames(df2)]
### Write new dataframe
write.csv(df3, 'hello.csv')