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Dragoș Moldovan-Grünfeld edited comment on ARROW-13887 at 10/6/21, 2:32 PM: ---------------------------------------------------------------------------- I think there might be a bit more than meets the eye to this issue, to the point that it becomes a different conversation (about the API of the function). Both `col_types` and `schema` arguments accept a `Schema` object, but the way they treat it are a bit different: * `schema` errors if the CSV file has column headers, while * `col_types` ignores it the column names. (although the documentation states that the names in the object and in the column headers *must* match, nothing happens if they don't) A slightly modified example: {code:java} library(arrow) share_data <- tibble::tibble( company = c("AMZN", "GOOG", "BKNG", "TSLA"), price = c(3463.12, 2884.38, 2300.46, 732.39) ) tf <- tempfile() write.csv(share_data, tf, row.names = FALSE) share_schema <- schema( company = utf8(), price = float64() ) # this errors read_csv_arrow(tf, schema = share_schema) # this works read_csv_arrow(tf, col_types = share_schema) conflict_col_names_schema <- schema( company_test = utf8(), price = float64() ) # this works, but as per the current documentation it should error, but # read_csv_arrow() simply ignores the mismatched column names # (Schema object vs CSV file) read_csv_arrow(tf, col_types = conflict_col_names_schema) unlink(tf){code} was (Author: dragosmg): I think there might be a bit more than meets the eye to this issue, to the point that it becomes a different conversation (about the API of the function). Both `col_types` and `schema` arguments accept a `Schema` object, but the way they treat it are a bit different: * `schema` errors if the CSV file has column headers, while * `col_types` ignores it the column names. (although the documentation states that the names in the object and in the column headers *must* match, nothing happens if they don't) A slightly modified example: {code:java} // code placeholder library(arrow) share_data <- tibble::tibble( company = c("AMZN", "GOOG", "BKNG", "TSLA"), price = c(3463.12, 2884.38, 2300.46, 732.39) ) tf <- tempfile() write.csv(share_data, tf, row.names = FALSE) share_schema <- schema( company = utf8(), price = float64() ) # this errors read_csv_arrow(tf, schema = share_schema) # this works read_csv_arrow(tf, col_types = share_schema) conflict_col_names_schema <- schema( company_test = utf8(), price = float64() ) # this works, but as per the current documentation it should error, but # read_csv_arrow() simply ignores the mismatched column names # (Schema object vs CSV file) read_csv_arrow(tf, col_types = conflict_col_names_schema) unlink(tf){code} > [R] Capture error produced when reading in CSV file with headers and using a > schema, and add suggestion > ------------------------------------------------------------------------------------------------------- > > Key: ARROW-13887 > URL: https://issues.apache.org/jira/browse/ARROW-13887 > Project: Apache Arrow > Issue Type: Improvement > Components: R > Reporter: Nicola Crane > Assignee: Dragoș Moldovan-Grünfeld > Priority: Major > Labels: good-first-issue > Fix For: 6.0.0 > > > When reading in a CSV with headers, and also using a schema, we get an error > as the code tries to read in the header as a line of data. > {code:java} > share_data <- tibble::tibble( > company = c("AMZN", "GOOG", "BKNG", "TSLA"), > price = c(3463.12, 2884.38, 2300.46, 732.39) > ) > readr::write_csv(share_data, file = "share_data.csv") > share_schema <- schema( > company = utf8(), > price = float64() > ) > read_csv_arrow("share_data.csv", schema = share_schema) > {code} > {code:java} > Error: Invalid: In CSV column #1: CSV conversion error to double: invalid > value 'price' > /home/nic2/arrow/cpp/src/arrow/csv/converter.cc:492 decoder_.Decode(data, > size, quoted, &value) > /home/nic2/arrow/cpp/src/arrow/csv/parser.h:84 status > /home/nic2/arrow/cpp/src/arrow/csv/converter.cc:496 > parser.VisitColumn(col_index, visit) {code} > The correct thing here would have been for the user to supply the argument > {{skip=1}} to {{read_csv_arrow()}} but this is not immediately obvious from > the error message returned from C++. We should capture the error and instead > supply our own error message using {{rlang::abort}} which informs the user of > the error and then suggests what they can do to prevent it. > > For similar examples (and their associated PRs) see > {color:#1d1c1d}ARROW-11766, and ARROW-12791{color} -- This message was sent by Atlassian Jira (v8.3.4#803005)