Did you try to do that inside you for loop ?
What you are doing is working, for each u value, you build the url and you read the html. Then you should extract the value you want.
library('rvest')
#> Le chargement a nécessité le package : xml2
#Specifying the url for desired website to be scraped
page <- list()
inshows = c("100","200","400")
for(u in inshows) {
url <- paste0('https://www.imdb.com/search/title?title_type=feature&release_date=2016-01-01,2016-12-31&count=100&start=', u,'&ref_=adv_nxt')
page[[u]] <- read_html(url) %>% html_nodes('.text-primary') %>% html_text()
}
page
#> $`100`
#> [1] "100." "101." "102." "103." "104." "105." "106." "107." "108." "109."
#> [11] "110." "111." "112." "113." "114." "115." "116." "117." "118." "119."
#> [21] "120." "121." "122." "123." "124." "125." "126." "127." "128." "129."
#> [31] "130." "131." "132." "133." "134." "135." "136." "137." "138." "139."
#> [41] "140." "141." "142." "143." "144." "145." "146." "147." "148." "149."
#> [51] "150." "151." "152." "153." "154." "155." "156." "157." "158." "159."
#> [61] "160." "161." "162." "163." "164." "165." "166." "167." "168." "169."
#> [71] "170." "171." "172." "173." "174." "175." "176." "177." "178." "179."
#> [81] "180." "181." "182." "183." "184." "185." "186." "187." "188." "189."
#> [91] "190." "191." "192." "193." "194." "195." "196." "197." "198." "199."
#>
#> $`200`
#> [1] "200." "201." "202." "203." "204." "205." "206." "207." "208." "209."
#> [11] "210." "211." "212." "213." "214." "215." "216." "217." "218." "219."
#> [21] "220." "221." "222." "223." "224." "225." "226." "227." "228." "229."
#> [31] "230." "231." "232." "233." "234." "235." "236." "237." "238." "239."
#> [41] "240." "241." "242." "243." "244." "245." "246." "247." "248." "249."
#> [51] "250." "251." "252." "253." "254." "255." "256." "257." "258." "259."
#> [61] "260." "261." "262." "263." "264." "265." "266." "267." "268." "269."
#> [71] "270." "271." "272." "273." "274." "275." "276." "277." "278." "279."
#> [81] "280." "281." "282." "283." "284." "285." "286." "287." "288." "289."
#> [91] "290." "291." "292." "293." "294." "295." "296." "297." "298." "299."
#>
#> $`400`
#> [1] "400." "401." "402." "403." "404." "405." "406." "407." "408." "409."
#> [11] "410." "411." "412." "413." "414." "415." "416." "417." "418." "419."
#> [21] "420." "421." "422." "423." "424." "425." "426." "427." "428." "429."
#> [31] "430." "431." "432." "433." "434." "435." "436." "437." "438." "439."
#> [41] "440." "441." "442." "443." "444." "445." "446." "447." "448." "449."
#> [51] "450." "451." "452." "453." "454." "455." "456." "457." "458." "459."
#> [61] "460." "461." "462." "463." "464." "465." "466." "467." "468." "469."
#> [71] "470." "471." "472." "473." "474." "475." "476." "477." "478." "479."
#> [81] "480." "481." "482." "483." "484." "485." "486." "487." "488." "489."
#> [91] "490." "491." "492." "493." "494." "495." "496." "497." "498." "499."
Created on 2019-01-16 by the reprex package (v0.2.1)
on way to do it using tidyverse
library(rvest)
#> Le chargement a nécessité le package : xml2
library(purrr)
#> Warning: le package 'purrr' a été compilé avec la version R 3.5.2
#>
#> Attachement du package : 'purrr'
#> The following object is masked from 'package:rvest':
#>
#> pluck
inshows = c("100","200","400")
urls <- glue::glue("https://www.imdb.com/search/title?title_type=feature&release_date=2016-01-01,2016-12-31&count=100&start={inshows}&ref_=adv_nxt")
urls
#> https://www.imdb.com/search/title?title_type=feature&release_date=2016-01-01,2016-12-31&count=100&start=100&ref_=adv_nxt
#> https://www.imdb.com/search/title?title_type=feature&release_date=2016-01-01,2016-12-31&count=100&start=200&ref_=adv_nxt
#> https://www.imdb.com/search/title?title_type=feature&release_date=2016-01-01,2016-12-31&count=100&start=400&ref_=adv_nxt
urls %>%
set_names(inshows) %>%
map(~ {
read_html(.x) %>%
html_nodes('.text-primary') %>%
html_text()
})
#> $`100`
#> [1] "100." "101." "102." "103." "104." "105." "106." "107." "108." "109."
#> [11] "110." "111." "112." "113." "114." "115." "116." "117." "118." "119."
#> [21] "120." "121." "122." "123." "124." "125." "126." "127." "128." "129."
#> [31] "130." "131." "132." "133." "134." "135." "136." "137." "138." "139."
#> [41] "140." "141." "142." "143." "144." "145." "146." "147." "148." "149."
#> [51] "150." "151." "152." "153." "154." "155." "156." "157." "158." "159."
#> [61] "160." "161." "162." "163." "164." "165." "166." "167." "168." "169."
#> [71] "170." "171." "172." "173." "174." "175." "176." "177." "178." "179."
#> [81] "180." "181." "182." "183." "184." "185." "186." "187." "188." "189."
#> [91] "190." "191." "192." "193." "194." "195." "196." "197." "198." "199."
#>
#> $`200`
#> [1] "200." "201." "202." "203." "204." "205." "206." "207." "208." "209."
#> [11] "210." "211." "212." "213." "214." "215." "216." "217." "218." "219."
#> [21] "220." "221." "222." "223." "224." "225." "226." "227." "228." "229."
#> [31] "230." "231." "232." "233." "234." "235." "236." "237." "238." "239."
#> [41] "240." "241." "242." "243." "244." "245." "246." "247." "248." "249."
#> [51] "250." "251." "252." "253." "254." "255." "256." "257." "258." "259."
#> [61] "260." "261." "262." "263." "264." "265." "266." "267." "268." "269."
#> [71] "270." "271." "272." "273." "274." "275." "276." "277." "278." "279."
#> [81] "280." "281." "282." "283." "284." "285." "286." "287." "288." "289."
#> [91] "290." "291." "292." "293." "294." "295." "296." "297." "298." "299."
#>
#> $`400`
#> [1] "400." "401." "402." "403." "404." "405." "406." "407." "408." "409."
#> [11] "410." "411." "412." "413." "414." "415." "416." "417." "418." "419."
#> [21] "420." "421." "422." "423." "424." "425." "426." "427." "428." "429."
#> [31] "430." "431." "432." "433." "434." "435." "436." "437." "438." "439."
#> [41] "440." "441." "442." "443." "444." "445." "446." "447." "448." "449."
#> [51] "450." "451." "452." "453." "454." "455." "456." "457." "458." "459."
#> [61] "460." "461." "462." "463." "464." "465." "466." "467." "468." "469."
#> [71] "470." "471." "472." "473." "474." "475." "476." "477." "478." "479."
#> [81] "480." "481." "482." "483." "484." "485." "486." "487." "488." "489."
#> [91] "490." "491." "492." "493." "494." "495." "496." "497." "498." "499."
Created on 2019-01-16 by the reprex package (v0.2.1)