[R] replacing percentage of values in data frame

[a217]

I've been looking for how to change a certain percentage of values in a data
frame, but I've been struggling to find information in R.

For example:

#################example data##############
> data
      V1    V2    V3  V4 V5  V6 V7
1   chr1   500   500 CHH  0 0.5  +
2   chr1   550   550 CHH  0 0.0  +
3   chr2   700   700 CHH  0 0.0  +
4   chr2  1000  1000 CHH  0 0.0  +
5   chr3   100   100 CHH  0 0.0  +
6   chr4   450   450  CG  0 0.0  +
7   chr5   450   450 CHH  0 0.0  +
8   chr5 50034 50034 CHG  0 0.0  +
9   chr7 50055 50055 CHG  0 0.0  +
10 chr10 50063 50063 CHH  0 0.0  +

> dput(data)
structure(list(V1 = structure(c(1L, 1L, 3L, 3L, 4L, 5L, 6L, 6L, 
7L, 2L), .Label = c("chr1", "chr10", "chr2", "chr3", "chr4", 
"chr5", "chr7"), class = "factor"), V2 = c(500L, 550L, 700L, 
1000L, 100L, 450L, 450L, 50034L, 50055L, 50063L), V3 = c(500L, 
550L, 700L, 1000L, 100L, 450L, 450L, 50034L, 50055L, 50063L), 
    V4 = structure(c(3L, 3L, 3L, 3L, 3L, 1L, 3L, 2L, 2L, 3L), .Label =
c("CG", 
    "CHG", "CHH"), class = "factor"), V5 = c(0L, 0L, 0L, 0L, 
    0L, 0L, 0L, 0L, 0L, 0L), V6 = c(0.5, 0, 0, 0, 0, 0, 0, 0, 
    0, 0), V7 = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
    1L), .Label = "+", class = "factor")), .Names = c("V1", "V2", 
"V3", "V4", "V5", "V6", "V7"), class = "data.frame", row.names = c(NA, 
-10L))
> 
############################

Say for instance, I'd like to change 20% of values in column 6 to '1'
instead of zero or whatever value may be currently present. How would I
approach this?

I am working with a large data frame and I need to replace values in one of
the columns for 10-20% of the entire dataset. I hope what I am trying to
convey is understandable to you.

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