Select every nth row from dataframe

Question

I have a data table and want to extract every fifth row from it to create a new table. Is there a command to achieve this?

Here is an sample of my data:

Answer 1

For a data frame df, you can get df.new as:

df.new = df[seq(1, nrow(df), 5), ]

This creates an index from row 1 to nrow (number of rows of the table) every 5 rows. You can play with the starting point and the 5 to extract other sequences.

Answer 2

If you want to extract 5,10...

newdf <- df[c(rep(FALSE,4),TRUE), ]

If 1,6,11,

newdf <- df[c(TRUE,rep(FALSE,4)), ]

Answer 3

One dplyr possibility for this task could be:

df %>%
 slice(which(row_number() %% 5 == 1))

  count Idf_Nr block
1     1   1233   B12
2     6    365   B12
3    11   1092   B12
4    16   1266   B12
5    21   1074   B12

Or:

df %>%
 filter(row_number() %% 5 == 1)