Replace value in data frame if value is greater or smaller

Question

I have problem manipulating data-frame in R. This is basic thing in R, but I can't find best command to do this type of things.

Dummy example

Var1 20 300  39
Var2 49  23  91
Var3  0 239 210

How can I replace value with 10 in column 2 if value is smaller than 10;
Or how to replace all values in data-frame with 100, if they are greater than 200?

Answer 1

You can use apply to replace all values greater than for example 200 in a whole data.frame

apply(df, 2, function(x) ifelse(x > 200, 100, x))

Note: if any columns are not numeric, all columns will be converted to character or factor. To avoid this, you can do the following. If you have a data.frame df with two numeric columns, columns 1 and 2, which you want to operate on, and two non-numeric columns, which you dont want to operate on, you could do this:

df <- cbind(apply(df[,1:2], 2, function(x) ifelse(x > 200, 100, x)), df[,3:4])

Edit after comment by @GregSnow:

It may be more useful to use lapply in this situation.

df[] <- lapply(df, function(x) ifelse(x>200, 100, x))

For anyone who didn't know before (including myself), by using df[] instead of only df the structure of df is kept as it was before (thanks @GregSnow for valuable information).