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# Subset by row number within magrittr chain

By : user2952420
Date : November 19 2020, 01:01 AM
I hope this helps you . Another option would be just using value = TRUE within grep (which will save you one extra operator)
code :
``````readLines(top_url) %>% grep("SitReps", ., value = TRUE)
``````
``````readLines(top_url) %>% `[`(grep("SitReps", .))
``````

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## Find N number subset in Array that sum to 0 [Subset Sum problem, that returns the subset]

By : user3131231
Date : March 29 2020, 07:55 AM
it helps some times Just make S[s] contain the list of numbers that make that sum when it is possible:
code :
``````Let S[i] = the list of numbers that make up that sum and false (or null, something distinct from an empty list) otherwise.

S[0] = empty list // we can always make sum 0: just don't choose any number
S[i] = null for all i != 0
for each number i in your input
for s = MaxSum downto i
if ( S[s - i] != null )
S[s] = S[s-i] with i added; // if we can make the sum s - i, we can also make the sum s by adding i to the sum s - i.
``````

## how to feed the result of a pipe chain (magrittr) to an object

By : Lee Sea Wuyhs
Date : March 29 2020, 07:55 AM
it fixes the issue This is a fairly simply question. But I couldn't find the answer per google/stackexchange and looking at the documentation of magrittr. How do you feed the result of a chain of functions which are connected via %>% to create a vector? , Try this:
code :
``````data.frame( x = c(1:3), y = (4:6)) %>% sum -> a
``````

## How to extract / subset an element from a list with the magrittr %>% pipe?

By : Farouk Touzi
Date : March 29 2020, 07:55 AM
should help you out Since the introduction of the %>% operator in the magrittr package (and it's use in dplyr), I have started to use this in my own work. , In v 1.5 of magrittr on CRAN you can use the %\$% operator:
code :
``````iris %\$%
Species %>%
levels
``````
``````iris %>%
with(Species %>% levels)
``````
``````iris %>%
with(Species) %>%
levels
``````
``````iris %>%
plot(Sepal.Length ~ Sepal.Width, data = .)
``````
``````iris %\$%
ts.plot(Sepal.Length)
``````

## Using magrittr to change a subset of values

By : user3666938
Date : March 29 2020, 07:55 AM
I wish did fix the issue. I have a time series dataframe with a day of the week column. I would like to replace all of the Mondays (day 1) that are holidays with a 6 for Sunday without breaking my pipeline using magrittr. , use %in% to make the index, then replace with mutate I guess:
code :
``````df %>% mutate(day=replace(day, date %in% as.POSIXct(holidays), 6))
``````

## How to add a row names to a data frame in a magrittr chain

By : Engel He
Date : March 29 2020, 07:55 AM
should help you out I want to do the opposite of: Convert row names into first column , You can use row.names<-:
code :
``````mtcars <- mtcars %>% `row.names<-`(as.character(1:nrow(mtcars)))
``````
``````df <- data.frame(x = 1:5, y = 2:6)
df <- df %>% `row.names<-`(letters[1:5])
df

#   x y
# a 1 2
# b 2 3
# c 3 4
# d 4 5
# e 5 6
``````