Combine characters list in R for-loop

February 24, 2023

I try to combine a list of characters, printed in r by a for-loop, using the function c(), but I can’t do it and cols list stay NULL.

cols <- 
 c(
   for(j in periods) {
     if(is.na(df[grep(j, df$Period),]$Scenario[[1]])) {
       print(j, collapse = ",")
   } else {
     for (k in ssp) {
       print(paste(j, k, sep="_", collapse = ","))
     }
   }  
 }
 )

# Console
[1] "1951-1980"
[1] "1981-2010"
[1] "2011-2040_ssp126"
[1] "2011-2040_ssp370"
[1] "2011-2040_ssp585"
[1] "2041-2070_ssp126"
[1] "2041-2070_ssp370"
[1] "2041-2070_ssp585"
[1] "2071-2100_ssp126"
[1] "2071-2100_ssp370"
[1] "2071-2100_ssp585"
> cols
NULL

I want to ask my loop to do this below automatically:

cols <- c("1951-1980","1981-2010","2011-2040_ssp126","2011-2040_ssp370","2011-2040_ssp585","2041-2070_ssp126","2041-2070_ssp370","2041-2070_ssp585","2071-2100_ssp126","2071-2100_ssp370","2071-2100_ssp585")

How can I ask to my loop to automatically run this?

Thank you for you help.

To help you,

# My data frame
> df <- map[sample(nrow(map), 30), ]
> dput(df)
df <- structure(list(rowname = c("fr2041-2070_ssp126_5521", "fr2071-2100_ssp370_9962", 
"fr2071-2100_ssp585_6140", "fr2041-2070_ssp126_10362", "fr2071-2100_ssp585_2461", 
"fr2071-2100_ssp370_5668", "fr2011-2040_ssp585_5251", "fr2041-2070_ssp370_7120", 
"fr2071-2100_ssp126_7171", "fr2041-2070_ssp126_6092", "fr2071-2100_ssp370_12266", 
"fr2041-2070_ssp370_4224", "fr2041-2070_ssp370_3195", "fr2071-2100_ssp585_5245", 
"fr2041-2070_ssp126_5228", "fr2071-2100_ssp370_3492", "fr1951-1980_13223", 
"fr2071-2100_ssp585_4505", "fr2041-2070_ssp585_6574", "fr1981-2010_9649", 
"fr1981-2010_8049", "fr2071-2100_ssp370_1269", "fr2041-2070_ssp126_4494", 
"fr2071-2100_ssp370_2894", "fr2071-2100_ssp585_3951", "fr2041-2070_ssp126_3324", 
"fr2071-2100_ssp585_4510", "fr2041-2070_ssp370_7156", "fr2071-2100_ssp585_3029", 
"fr2041-2070_ssp585_2580"), Period = c("2041-2070", "2071-2100", 
"2071-2100", "2041-2070", "2071-2100", "2071-2100", "2011-2040", 
"2041-2070", "2071-2100", "2041-2070", "2071-2100", "2041-2070", 
"2041-2070", "2071-2100", "2041-2070", "2071-2100", "1951-1980", 
"2071-2100", "2041-2070", "1981-2010", "1981-2010", "2071-2100", 
"2041-2070", "2071-2100", "2071-2100", "2041-2070", "2071-2100", 
"2041-2070", "2071-2100", "2041-2070"), Scenario = c("ssp126", 
"ssp370", "ssp585", "ssp126", "ssp585", "ssp370", "ssp585", "ssp370", 
"ssp126", "ssp126", "ssp370", "ssp370", "ssp370", "ssp585", "ssp126", 
"ssp370", NA, "ssp585", "ssp585", NA, NA, "ssp370", "ssp126", 
"ssp370", "ssp585", "ssp126", "ssp585", "ssp370", "ssp585", "ssp585"
)), row.names = c(NA, -30L), class = c("data.table", "data.frame"
))

>Solution :

Here is one option to do this in for loop – print doesn’t have a return value

cols <- character(0)
 for(j in periods) {
     if(is.na(df[grep(j, df$Period),]$Scenario[[1]])) {
       cols <- c(cols, j)
   } else {
     for (k in ssp) {
       cols <- c(cols, paste(j, k, sep="_", collapse = ","))
     }
   }  
 }