r collapsing data from multiple columns into one - r

Question

I know there are many questions on this topic so I apologize if this is a duplicate question. I'm trying to collapse multiple columns in a data set into one column:
Assuming this is the structure of the dataset I am working with,
df <- data.frame(
cbind(
variable_1 = c('Var1', NA, NA,'Var1'),
variable_2 = c('Var2', 'No', NA, NA),
variable_3 = c(NA, NA, 'Var3', NA),
variable_4 = c(NA, 'Var4', NA, NA),
variable_5 = c(NA, 'No', 'Var5', NA),
variable_6 = c(NA, NA, 'Var6', NA)
))
variable_1 variable_2 variable_3 variable_4 variable_5 variable_6
Var1 Var2 NA NA NA NA
NA No NA Var4 No NA
NA NA Var3 NA Var5 Var6
Var1 NA NA NA NA NA
What I am expecting is a one column variable_7 like this
variable_1 variable_2 variable_3 variable_4 variable_5 variable_6 variable_7
Var1 Var2 NA NA NA NA Var1, Var2
NA No NA Var4 No NA Var4
NA NA Var3 NA Var5 Var6 Var3, Var5, Var6
Var1 NA NA NA NA NA Var1

Answer 1

df$variable_7 <- apply(df, 1, function(x) paste(x[!is.na(x) & x != "No"], collapse = ", "));
df;
# variable_1 variable_2 variable_3 variable_4 variable_5 variable_6
#1 Var1 Var2 <NA> <NA> <NA> <NA>
#2 <NA> No <NA> Var4 No <NA>
#3 <NA> <NA> Var3 <NA> Var5 Var6
#4 Var1 <NA> <NA> <NA> <NA> <NA>
# variable_7
#1 Var1, Var2
#2 Var4
#3 Var3, Var5, Var6
#4 Var1
Explanation: Use apply and paste(..., collapse = ", ") to concatenate all row entries (except NAs and "No"s) and store in new column variable_7.
Sample data
df <- data.frame(
cbind(
variable_1 = c('Var1', NA, NA,'Var1'),
variable_2 = c('Var2', 'No', NA, NA),
variable_3 = c(NA, NA, 'Var3', NA),
variable_4 = c(NA, 'Var4', NA, NA),
variable_5 = c(NA, 'No', 'Var5', NA),
variable_6 = c(NA, NA, 'Var6', NA)
))

Answer 2

I gather that if there are n rows then objective is to create a an n-vector of comma-separated character strings of those values in each row that contain the characters Var. (If you intended some other criterion for separating the desired and undesired values then change the grep accordingly.)
apply(df, 1, function(x) toString(grep("Var", x, value = TRUE)))
## [1] "Var1, Var2" "Var4" "Var3, Var5, Var6" "Var1"

Answer 3

A solution using dplyr. df4 is the final output. Please see how I created the data frame df. The cbind is not required, and it would be great to add stringsAsFactors = FALSE to prevent the creation of factor columns.
library(dplyr)
library(tidyr)
df2 <- df %>% mutate(ID = 1:n())
df3 <- df2 %>%
gather(Variable, Value, -ID, na.rm = TRUE) %>%
filter(!Value %in% "No") %>%
group_by(ID) %>%
summarise(variable_7 = toString(Value))
df4 <- df2 %>%
left_join(df3, by = "ID") %>%
select(-ID)
df4
# variable_1 variable_2 variable_3 variable_4 variable_5 variable_6 variable_7
# 1 Var1 Var2 <NA> <NA> <NA> <NA> Var1, Var2
# 2 <NA> No <NA> Var4 No <NA> Var4
# 3 <NA> <NA> Var3 <NA> Var5 Var6 Var3, Var5, Var6
# 4 Var1 <NA> <NA> <NA> <NA> <NA> Var1
DATA
df <- data.frame(
variable_1 = c('Var1', NA, NA,'Var1'),
variable_2 = c('Var2', 'No', NA, NA),
variable_3 = c(NA, NA, 'Var3', NA),
variable_4 = c(NA, 'Var4', NA, NA),
variable_5 = c(NA, 'No', 'Var5', NA),
variable_6 = c(NA, NA, 'Var6', NA),
stringsAsFactors = FALSE
)

Answer 4

Using a data.table 'reshap'-ing approach rather than a loop/apply
library(data.table)
setDT(df)
df[, id := .I][
melt(df, id.vars = "id")[grepl("Var", value), .(variable_7 = paste0(value, collapse = ",")), by = .(id)]
, on = "id"
, nomatch = 0
][order(id)]
# variable_1 variable_2 variable_3 variable_4 variable_5 variable_6 id variable_7
# 1: Var1 Var2 NA NA NA NA 1 Var1,Var2
# 2: NA No NA Var4 No NA 2 Var4
# 3: NA NA Var3 NA Var5 Var6 3 Var3,Var5,Var6
# 4: Var1 NA NA NA NA NA 4 Var1