For loop with an index inside a string in R

Question

I have a rather simple problem but somehow I cannot solve it.

So I have a dataset with a column cycle with rows cycle1, cycle2, cycle3. I want to replace e.g. the word cycle1 with just the number 1. How to somehow separate the index i from the string cycle?

for (i in 1:3){
   data$cycle[data$cycle=="cyclei"]<-i
}

with stringr you can do data$indice <- str_extract(data$cycle, "\\d") — s.brunel
– s.brunel, Commented Mar 5, 2018 at 15:22

G. Grothendieck · Accepted Answer · 2018-03-05 15:21:31Z

2

Replace "cycle" with the empty string and convert to numeric:

data <- data.frame(cycle = c("cycle2", "cycle1", "cycle3")) # sample input

transform(data, cycle = as.numeric(sub("cycle", "", cycle)))

giving:

answered Mar 5, 2018 at 15:21

G. Grothendieck

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1 Comment

De Novo Over a year ago

if the point is to get the actual index value of the element (based on its position in the vector) and use that for the row name, please don't do it this way :) If the point is to extract a portion of the string, then this is a good answer.

Cristian E. Nuno · Accepted Answer · 2018-03-05 15:52:31Z

2

Use `gsub()`

# load data 
df <- data.frame( cycle = c( "cycle1", "cycle2", "cycle3" ), stringsAsFactors = FALSE )

# Identify the pattern and replace with nothing
# and cast the values as numeric
df$cycle <- as.numeric( gsub( pattern = "cycle", replacement = "", x = df$cycle ) )

# view results
df
#  cycle
# 1    1
# 2    2
# 3    3

# end of script #

edited Mar 5, 2018 at 15:52

answered Mar 5, 2018 at 15:22

Cristian E. Nuno

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For loop with an index inside a string in R

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Use `gsub()`

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Use `gsub()`